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Buick Roadmaster Estate Wagon 1994 - G - TESTS W/CODES - 5.7L 1994 ENGINE PERFORMANCE General Motors Corp. Self-Diagnostics - 5.7L V8
Buick Roadmaster Estate Wagon 1994 - INTRODUCTION
Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, perform checks and inspections covered in BASIC TESTING article in this section. Failure to do so may result in lost diagnostic time.
If no faults were found while performing BASIC TESTING , proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no fault codes or only a non-running Code 12 is present and driveability problems exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 - SELF-DIAGNOSTIC SYSTEM
NOTE: Powertrain Control Module (PCM) is also be referred to as Electronic Control Module (ECM) in some diagnostic charts and figures. Terms are used interchangeably.
Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate SERVICE ENGINE SOON light located on instrument panel. SERVICE ENGINE SOON light is also be referred to as the Malfunction Indicator Light (MIL). When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as hard failures or as intermittent failures.
Buick Roadmaster Estate Wagon 1994 - HARD FAILURES
Hard failures cause SERVICE ENGINE SOON light to glow and remain on until malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control module will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely encounter degraded driveability.
Buick Roadmaster Estate Wagon 1994 - INTERMITTENT FAILURES
Intermittent failures cause SERVICE ENGINE SOON light to flicker or glow and go out about 10 seconds after intermittent fault goes away. Corresponding trouble code, however, will be retained in control module memory. If related fault does not reoccur within 50 engine starts, related trouble code will be erased from control module memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 - DIAGNOSTIC PROCEDURE
Diagnosis of computerized engine control system should be performed in following order:
- Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See BASIC TESTING article in this section.
- If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES article in this section.
- If no trouble codes are present and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will help identify proper system or component to check in SYSTEM/COMPONENT TESTS - 5.7L article in this section.
- After necessary repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
NOTE: For information on retrieving codes using a scan tester, refer to user and reference manuals supplied with tester.
Buick Roadmaster Estate Wagon 1994 - RETRIEVING CODES (NON-SCAN)
NOTE: On models using a 12-terminal DLC (previously referred to as the ALDL), if a wire is present at terminal "B", inserting a jumper wire into test and ground terminals of DLC with engine running will cause fuel injected vehicles to enter field service mode. Flashes of SERVICE ENGINE SOON light will not indicate codes if this is done. See FIELD SERVICE MODE CHECK in BASIC TESTING article in the ENGINE PERFORMANCE section. On models not using a 12-terminal DLC or not having a wire present in terminal "B", codes must be retrieved using a hand-held scan tester.
Buick Roadmaster Estate Wagon 1994 DATA LINK CONNECTOR (DLC) TEST TERMINALS
Application Ground/Test 12-Pin DLC "A" & "B"
- Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate DLC attached to control module wiring harness. Most DLC's are located under dash on driver side of vehicle. For exact location of DLC, proceed to COMPONENT LOCATIONS in the SYSTEM/COMPONENT TESTS - 5.7L article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC. See Fig. 1 .
- SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed or SERVICE ENGINE SOON light does not glow, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from DLC connector.
Fig. 1: Buick Roadmaster Estate Wagon 1994 - Component Locations - ALDL/DLC Connector Terminal ID
Buick Roadmaster Estate Wagon 1994 - READING TROUBLE CODES
Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light or by reading digital display on a scan tester. Scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .
NOTE: When using most scan testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.
If scan tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" (if a wire is present) of DLC with ignition on and engine off. See Fig. 1 . For example, "FLASH, FLASH, pause, FLASH, longer pause" identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code. Trouble codes are displayed starting with lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as DLC test terminal is grounded.
NOTE: Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.
Buick Roadmaster Estate Wagon 1994 - TROUBLE CODE DEFINITION
Buick Roadmaster Estate Wagon 1994 ECM/PCM TROUBLE CODE DEFINITION
Code No. Circuit Affected 11 MIL 12 (1) No RPM Reference Pulse 13 Left Heated Oxygen Sensor Circuit Open 14 Coolant Temperature Sensor Signal Voltage Low 15 Coolant Temperature Sensor Signal Voltage High 16 Low Resolution Pulse 18 Injector Circuits 21 TPS Signal Voltage High 22 TPS Signal Voltage Low 23 Intake Air Temperature Sensor Signal Voltage High 24 Vehicle Speed Sensor 25 Intake Air Temperature Sensor Signal Voltage Low 26 Quad-Driver Error 27 EGR Vacuum Control Signal Solenoid Valve Circuit 28 Transmission Range Pressure Switch Assembly Fault 29 Secondary Air Injection Pump Circuit 32 EGR System Error 33 MAP Sensor Signal Voltage High 34 MAP Sensor Signal Voltage Low 36 High Resolution Pulse 37 TCC Brake Switch Stuck ON 38 TCC Brake Switch Stuck OFF 41 Opti-Spark Open Circuit 42 Opti-Spark Circuit Shorted Or Grounded 43 ESC (Knock Sensor) Error 44 Left Heated Oxygen Sensor Lean Exhaust Indication 45 Left Heated Oxygen Sensor Rich Exhaust Indication 46 Pass-Key Circuit 47 Knock Sensor Circuit Or Module Missing 48 MAF Sensor 50 System Voltage Low 51 Faulty PROM, MEM-CAL Or ECM/PCM 53 System Overvoltage 55 Fuel Lean Monitor 58 Transmission Fluid Temp. High 59 Transmission Fluid Temp. Low 63 Right Heated Oxygen Sensor Circuit Open 64 Right Heated Oxygen Sensor Lean Exhaust Indication 65 Right Heated Oxygen Sensor Rich Exhaust Indication 66 A/C Pressure Sensor Open Or Shorted 67 A/C Pressure Sensor/Clutch Problem 68 A/C Relay Circuit Shorted 69 A/C Clutch Circuit 70 A/C Clutch Relay Driver Circuit 72 VSS Signal Loss 73 Pressure Control Solenoid Circuit (Current Error) 75 Transmission System Voltage Low 77 Primary Cooling Fan Relay Control Circuit 78 Secondary Cooling Fan Relay Control Circuit 79 Transmission Fluid Overtemp 80 Transmission Component Slipping 81 Transmission 2-3 Error 82 Transmission 1-2 Error 84 Transmission 3-2 Error 85 TCC Stuck On (A/T) 90 TCC Solenoid Circuit 95 Change Oil Light Circuit 96 Low Oil Light Circuit 97 VSS Output Circuit
(1) Display of a Code 12 is normal when reference pulses are not being received by control module (engine not running).
NOTE: Use trouble code charts only if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists).
Buick Roadmaster Estate Wagon 1994 - HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes:
- Enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See CLEARING TROUBLE CODES .
- Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
- If SERVICE ENGINE SOON light comes on, enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Oxygen sensor related codes may require a road test to reset hard failure after trouble codes were cleared.
- If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.
Buick Roadmaster Estate Wagon 1994 - CLEARING TROUBLE CODES
NOTE: On models not utilizing a 12-terminal DLC or if no wire is present in terminal "B", codes are cleared using a scan tester.
Turn ignition switch to ON position, and ground diagnostic test terminal "B" at DLC. See Fig. 1 . Turn ignition switch to OFF position, and remove control module fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, pigtail at battery can be disconnected. When power to ECM is remove, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.
Buick Roadmaster Estate Wagon 1994 - ECM/PCM LOCATION
On most models, engine control module is located behind right or left side of dash or behind right or left kick panel. See COMPONENT LOCATIONS in SYSTEM/COMPONENT TESTS - 5.7L article in this section.
Buick Roadmaster Estate Wagon 1994 - DIAGNOSTIC MATERIALS Diagnostic Aids
Diagnostic aids (located in many trouble code charts) are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.
Buick Roadmaster Estate Wagon 1994 - Field Service Mode Check (If Available)
If DLC test terminal "B" is grounded with engine running, SERVICE ENGINE SOON light will indicate operational mode of engine. This test confirms proper operation of fuel system and verifies "closed loop" operation. Clear codes and perform this test after any repair is completed. Some models require the use of a scan tester to enter field service mode. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
Buick Roadmaster Estate Wagon 1994 - SPECIAL TOOLS (DIAGNOSTIC)
NOTE: A scan tester plugged into DLC may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M"). This can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN DATA .
Computerized engine control system is most easily diagnosed using scan tester; however, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.
Buick Roadmaster Estate Wagon 1994 - SCAN TESTER USAGE
NOTE: Before connecting scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received will be accurate. This is done by performing DIAGNOSTIC CIRCUIT CHECK located in BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit check, information received may be invalid.
Scan tester is a specialized tester which, when plugged into DLC, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.
Scan tester cuts down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA. They may also furnish information on output device (solenoids and motors) status. However, status parameters only indicate output signals have been sent to devices by control module; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light. Vehicles utilizing a 16-terminal DLC or 12-terminal DLC with terminal "B" not used, must use a scan tester for retrieving codes or enter Field Service Mode.
NOTE: Code 12 should always exist when DLC terminal "B" is grounded with key on and engine not running, but it may not be indicated by all makes of scan testers.
A problem may exist even if trouble codes are not present. About 80 percent of driveability problems occur without trouble codes. Sensors that are out of calibration will not set a trouble code but will cause driveability problems.
Using a scan tester is the easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA .
NOTE: If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove tester, turn ignition on and ground DLC test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by scan tester.
Buick Roadmaster Estate Wagon 1994 - SCAN DATA
NOTE: Information contained in following tables is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated a minimum of every 1 1/4 seconds. On systems using P-4 computers, parameter updates are more frequent. Not all devices and systems are used on all models; following lists only represent most commonly used parameters. For additional information, refer to owner manual furnished with tester.
Buick Roadmaster Estate Wagon 1994 MULTIPORT FUEL INJECTION (MFI)
Tester Position Units Measured Nominal Value A/C Clutch On/Off Off (On With A/C) A/C Request Yes/No No/Yes (With Request) AIR Divert Sol. On/Off On (Air To Switching Sol.); Off (Air To Atmosphere) AIR Switching Sol. On/Off On (To Exhaust Manifold); Off (To Catalytic Converter) BARO Volts 3.0-4.5 Battery Voltage Volts 13.5-14.5 Block Learn (LT) Counts 118-138 (128 Normal) Canister Purge Sol. On/Off On/Engine Cold (Idle Some) Clear Flood On/Off See Tester Manual Coolant Fan(s) On/Off Off Below 216?F (102?C) Coolant Temp. ?C 85-105? (Norm. Temp.) Crank RPM RPM 100-900 Cross Counts Counts 0-255 EGR Solenoid On/Off On When Energized EGR Duty Cycle 0-100% 0/Closed; 100/Fully Open Fan Relay On/Off On When Energized Fan Request On/Off On With Request Fuel Back-Up Yes/No Yes When Engaged IAC Counts 0-50 Ignition/Crank On/Off On With Ignition/Crank Injector Pulse Width Mil./Sec .8-3.0 Integrator (ST) Counts 110-145 (128 Normal) Knock Retard Counts 0-255 Knock Signal Yes/No Yes When Knock Exists MAT (IAT) ?C 10-90? MAP Volts 1.0 (Idle) to 4.5 (WOT) "Open/Closed Loop Status" Ol/Cl Closed/Open During Extended Idle O2 Sensor Millivolts 100 (Lean) To 999 (Rich) P/N Switch P/N/RDL Park/Neutral P/S Switch Norm/Hi Normal PROM I.D. PROM # Original Factory Number RPM RPM Spec. +/-25 RPM Drive (A/T); Spec. +/-50 RPM Neut. (M/T) Spark Advance Degrees Varies TCC On/Off Off (On With Command) TP Sensor Volts 1.25 (Idle) To 5.00 (WOT) Throttle Angle 0-100% 0 (Idle) To 100 (WOT) Trouble Codes Code No. No Codes Upshift Light (M/T) On/Off Off VSS Or MPH MPH 0-Actual 1st Gear Switch On/Off On/1st Gear Only 3rd Gear Switch On/Off On/3rd & 4th Gear 4th Gear Switch On/Off On/4th Gear
Buick Roadmaster Estate Wagon 1994 - ECM/PCM CODE CHARTS
NOTE: In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp.
Buick Roadmaster Estate Wagon 1994 - CODE 11, MALFUNCTION INDICATOR LIGHT
MIL should always be on steady with ignition on and engine stopped. Ignition voltage is supplied directly to bulb. PCM turns on light by providing a path to ground.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If MIL driver circuit or ignition feed circuit to bulb is open, MIL will not illuminate.
- Jumper Harness (J 35616-A) should be used instead of directly probing harness. This will prevent damage to harness.
- MIL should go off after engine starts. If it does, problem is not present at this time. If light does not go off, drive circuit is shorted to ground or PCM is faulty.
- If other codes are also displayed, use other code charts first, then restart at beginning of this chart.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If ignition feed circuit is suspected of being open, check and see if other bulbs on that circuit illuminate. Code 11 will cause MIL to remain on, even if malfunction clears.
Buick Roadmaster Estate Wagon 1994 - CODE 13, OPEN LEFT HEATED OXYGEN SENSOR CIRCUIT
NOTE: The 5.7L (VIN P) engine is equipped with 2 oxygen sensors. On this model, code will set if the left sensor circuit is open. Code 63 will set if the right sensor circuit is open. Oxygen sensors use a heating element. Heating element is not controlled by PCM.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This tests if problem still exists. Vehicle cannot enter "closed loop" mode if oxygen sensor circuit is open. Code indicates an open in O2 sensor circuit. Code will set if Engine is at normal operating temperature, neither Code 21 nor Code 22 is stored, oxygen sensor voltage is constant within a specified range (.34-.55 volt), throttle angle is greater than idle, a precalibrated amount of time has elapsed since start-up and all conditions have existed for a precalibrated amount of time.
- Determines if oxygen sensor, wiring or control module is at fault. If wiring is good, grounding oxygen sensor wire will cause .45 volt reference supplied by control module to pull low.
- This tests oxygen sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Control module will not go into closed loop if code is set. Code may set if vehicle runs out of fuel or stalls while vehicle is in motion. If oxygen sensor ground becomes loose, a false oxygen sensor reading will occur. This can result in a Code 13 being set. On models equipped with an oxygen sensor heating element, element resistance should be 3.5-14 ohms.
Buick Roadmaster Estate Wagon 1994 CODE 13 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Left O2 Signal C20 Purple/White Left O2 Ground C19 Tan/White
Buick Roadmaster Estate Wagon 1994 - CODE 14, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE LOW
- For shared sensor ground tie-offs, see appropriate diagram under WIRING DIAGRAMS .
NOTE: This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.
- Code indicates control module has seen low coolant sensor voltage signal (high temperature) at control module terminal for a precalibrated period of time. This checks if conditions for code still exist.
- This tests for grounded sensor signal line between control module and coolant sensor.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
After engine is started, temperature should rise steadily to about 190?F (88?C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When code is set, control module will turn on electric cooling fan(s) if equipped.
Buick Roadmaster Estate Wagon 1994 CODE 14 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color CTS Signal C25 Yellow CTS Ground B16 Purple
Buick Roadmaster Estate Wagon 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 15, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE HIGH
- For shared sensor ground tie-offs, see appropriate diagram in WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code indicates control module has seen high resistance in coolant sensor circuit. This could be due to high resistance (cold temperature) or high voltage at coolant sensor terminal at control module for a precalibrated period of time. This checks if conditions for code still exist.
- This test simulates a low voltage condition. If control module recognizes low voltage signal, scan tester will display greater than 130?C. This indicates control module and wiring are not at fault.
- This test determines if coolant sensor ground or signal circuit is open.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
After engine is started, temperature should rise steadily to about 190?F (88?C) and then stabilize when thermostat opens. At normal operating temperature, voltage at control module sensor signal line should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When code is set, control module will turn on electric cooling fan(s) if equipped.
Buick Roadmaster Estate Wagon 1994 CODE 15 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color CTS Signal C25 Yellow CTS Ground B16 Purple
Buick Roadmaster Estate Wagon 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 16, OPTI-SPARK IGNITION SYSTEM LOW RESOLUTION PULSE
Ignition system supplies 2 timing inputs to PCM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (4 pulses per camshaft revolution). PCM can determine if either timing input is not being received by comparing inputs. If PCM detects high resolution pulse without detecting low pulse, Code 16 will set. Reference signal on resolution line toggles between zero and 5 volts as camshaft turns.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If engine starts at this time, code is intermittent.
- This step determines if PCM is sending out a signal to distributor for processing. If this signal is not available or is shorted to ground or voltage, distributor cannot ground it to produce reference pulses.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
An open, a short to voltage, a short to ground or a defective sensor inside distributor can prevent reference voltage from pulsing at PCM resolution terminal. If Code 16 does not reset and vehicle still does not start, refer to NO START - ENGINE CRANKS OKAY in the BASIC TESTING article in this section.
Buick Roadmaster Estate Wagon 1994 - CODE 18, INJECTOR CIRCUIT
Injectors are provided voltage when ignition is on. PCM energizes injectors by providing an individual ground for each injector. Injectors are energized on the intake stroke of each cylinder. PCM continuously monitors voltage on each driver circuit. When PCM detects a voltage that is out of range, Code 18 will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Injector fuses are located in the underhood electrical center.
- Performing an injector balance test will determine which injector circuit is faulty.
- See mini-schematic to determine which fuse powers injector banks.
- When checking injector resistance, injector should be cold.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If an injector is disconnected and then reconnected while engine is running, injector driver is disabled for a predetermined time and Code 18 will set. When driver is disabled, an engine misfire will be evident.
Buick Roadmaster Estate Wagon 1994 - CODE 21, THROTTLE POSITION SENSOR SIGNAL VOLTAGE HIGH
- For shared sensor ground tie-offs, see appropriate diagram in WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test checks if code is result of a hard failure or an intermittent condition.
- This test simulates a low-voltage condition. If control module recognizes change of state, control module and wiring are okay.
- This step isolates a faulty sensor, control module or open sensor ground circuit. If sensor ground is shared by another sensor, an accompanying code related to that sensor may exist.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 CODE 21 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color TPS Signal C22 Dark Blue TPS Ground B6 Black TPS Reference B28 Gray
Buick Roadmaster Estate Wagon 1994 - CODE 22, THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW
- For shared sensor ground tie-offs, see appropriate diagram in the WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test checks if code is result of a hard failure or an intermittent condition.
- This test simulates conditions for setting code. If control module recognizes change of state, control module and wiring are okay.
- This simulates a high signal voltage to check for an open in TPS signal line to control module. Scan tester should recognize this signal and display high TPS voltage.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 CODE 22 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color TPS Signal C22 Dark Blue TPS Ground B6 Black TPS Reference B28 Gray
Buick Roadmaster Estate Wagon 1994 - CODE 23, IAT SENSOR SIGNAL VOLTAGE HIGH
- For shared sensor ground tie-offs, see appropriate diagram in the WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is result of a hard failure or an intermittent condition. Code will set if engine has been running for a precalibrated period of time, has reached operating temperature and signal voltage indicates a intake air temperature less than -22?F (-30?C).
- This simulates conditions for setting code. If scan tester displays a high temperature, control module and wiring are not at fault.
- This checks for continuity of sensor signal and ground circuits. If ground circuit is shared by other sensors and ground circuit is open, accompanying codes related to those sensors may be present.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If engine is allowed to cool overnight, coolant and IAT sensor values should be close to each other when measured by scan tester. Code will result if signal and ground circuits become open. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Buick Roadmaster Estate Wagon 1994 CODE 23 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color IAT Signal C21 Tan IAT Ground B6 Black
Buick Roadmaster Estate Wagon 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 24, VEHICLE SPEED SENSOR
Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than 2 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 24 sets when MPH reads zero, transmission is not in Park or Neutral, engine speed indicates vehicle is in a cruise mode (1200-4400) RPM, TPS indicates closed throttle and MAP sensor senses high manifold vacuum. All of these conditions must be met for 2-5 seconds. PM generator only produces a voltage signal if drive wheels are turning greater than 2 MPH.
- Before replacing control module, PROM/MEM-CAL should be checked for correct application.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
A faulty or misadjusted park/neutral switch may set a false Code 24. Use scan tester to check for proper signal in Drive while wiggling shifter. Code 24 may set if vehicle is power braked (brakes applied and throttle depressed) for more than 10 seconds.
Buick Roadmaster Estate Wagon 1994 - CODE 25, IAT SENSOR SIGNAL VOLTAGE LOW
- For shared sensor ground tie-offs, see appropriate diagram in the WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is hard failure or intermittent condition. Code 25 will set if a IAT temperature greater than 266?F (130?C) is sensed for more than a precalibrated period.
- This simulates condition for Code 23. If control module recognizes open circuit and scan tester displays temperature of less than -30?C, control module and wiring are okay.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If engine is allowed to cool overnight, coolant temperature sensor and IAT sensor values should be close to each other when measured by a scan tester. A Code 25 will result if sensor signal circuit is shorted to ground. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Buick Roadmaster Estate Wagon 1994 CODE 25 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAT Signal C21 Tan MAT Ground B6 Black
Buick Roadmaster Estate Wagon 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 26, CANISTER PURGE SOLENOID
Solenoid is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When solenoid is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 26 will set if the PCM detects the wrong voltage potential. Test will determine if solenoid can be controlled by PCM.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative solenoid.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 27, EGR SOLENOID VALVE
Ignition voltage is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When solenoid is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 27 will set if the PCM detects the wrong voltage potential. Test will determine if solenoid can be controlled by PCM.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative solenoid.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 28, TRANSMISSION RANGE PRESSURE SWITCH
Transmission range pressure switch assembly consists of 5 pressure switches (2 normally closed, 3 normally open), and a fluid temperature sensor combined into one unit and mounted on the valve body. PCM supplies voltage to each range signal. By grounding one or more of these circuits through various combinations of pressure switches, PCM detects which manual valve position has been selected. With ignition on and engine off, Park/Neutral will be indicated. Code 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks indicated range signal to valve position signal actually selected.
- Checks for correct voltage from PCM to transmission external connector.
- Checks for short to ground in any one of the 3 valve position circuits.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Code will set if PCM detects one of 2 illegal combinations. Check all connections for good contact.
Buick Roadmaster Estate Wagon 1994 - CODE 29, SECONDARY AIR INJECTION
Ignition voltage is supplied voltage when ignition is on. PCM controls air pump relay by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 29 will set if the PCM detects the wrong voltage potential. Test will determine if relay can be controlled by PCM.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 32, EGR SYSTEM ERROR
EGR vacuum is regulated by an PCM-controlled, normally closed solenoid. PCM will turn EGR on and off (duty cycle) by grounding and ungrounding solenoid drive circuit. Duty cycle is calculated by PCM based on coolant temperature, airflow and engine RPM. PCM will check EGR operation when vehicle speed is 16-32 MPH, MAP is within calibrated range, throttle angle is zero percent and vehicle is coasting.
NOTE: Test numbers refer to numbers on diagnostic chart.
- See Following:
- Plugged Intake Passage:
Shut off engine, and remove EGR valve. Plug exhaust side port using a shop rag or suitable plug. Attempt to start engine. If engine runs at a very high idle (up to 3000 RPM is possible) or if engine starts and stalls, EGR intake passage is not plugged. If vehicle starts and idles normally, intake side passage is plugged. - Plugged Exhaust Passage:
With EGR valve removed, plug intake manifold side passage using a suitable plug. Start engine and listen for exhaust noise. If no exhaust gas escapes from open EGR port, exhaust passage is plugged.
- Plugged Intake Passage:
- Using Tech 1 tester, EGR solenoid should energize and allow vacuum to be applied to gauge. Vacuum at gauge may or may not slowly bleed off; however, gauge is able to read amount of vacuum being applied.
- Upon exiting field service mode, gauge vacuum should bleed off through a vent in solenoid. Pump gauge vacuum may or may not bleed off; this does not indicate a problem.
- This test determines if electrical control part of system is at fault or if connector or solenoid is at fault.
- EGR valves used with this engine are stamped "P" for positive backpressure or "N" for negative backpressure. Proceed to appropriate chart for valve being tested.
- Remaining tests check ability of EGR valve to interact with exhaust system. This system uses a negative backpressure EGR valve which will hold vacuum with engine off.
- When engine is started, exhaust backpressure at base of EGR valve should open valve's internal bleed. This will vent applied vacuum, allowing valve to seat.
Fig. 35: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 32 Flow Chart (1 of 2)
Fig. 36: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 32 Flow Chart (2 of 2)
Buick Roadmaster Estate Wagon 1994 - CODE 33, MAP SENSOR SIGNAL VOLTAGE HIGH
- For shared sensor reference and shared sensor ground tie -offs, see appropriate diagram in the WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test confirms Code 33 and determines if it is result of a hard failure or an intermittent condition. Code 33 will set when voltage signal reading is too high for greater than a precalibrated period of time, TPS voltage indicates throttle is closed and neither Code 21 nor 22 is present.
- This step simulates conditions for a Code 34. If control module recognizes and sets Code 34, low MAP signal, control module and 5-volt reference and MAP signal circuits are not at fault. If ground circuit is shared with other sensors and ground circuit becomes open, additional codes related to these sensors may be set.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparison of BARO readings from a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within .4 volt. Code 33 will result if ground circuit is open, MAP signal circuit is shorted to voltage or to 5-volt reference circuit.
Buick Roadmaster Estate Wagon 1994 CODE 33 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAP Signal C23 Light Green MAP Ground B16 Purple MAP Reference B29 Gray
Buick Roadmaster Estate Wagon 1994 - CODE 34, MAP SENSOR SIGNAL VOLTAGE LOW
- For shared sensor reference and shared sensor ground tie -offs, see appropriate diagram in WIRING DIAGRAMS section.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This confirms Code 34 and determines if code was caused by a hard failure or an intermittent fault. Code 34 will set when ignition is on and MAP signal voltage is low. On some systems, engine must be running to set code.
- Jumpering MAP signal to 5-volt reference at MAP harness connector will determine if sensor is at fault or if a problem exists with control module or wiring.
- Scan tester may not display 12 volts. Control module recognizes voltage as greater than 4 volts (high MAP voltage signal), indicating control module and MAP signal circuit are not at fault.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparing BARO readings with a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within .4 volt. A Code 34 will also result if 5-volt reference and MAP signal circuits are open or shorted to ground.
Buick Roadmaster Estate Wagon 1994 CODE 34 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color MAP Signal C11 Light Green MAP Ground D2 Purple MAP Reference C14 Gray
Buick Roadmaster Estate Wagon 1994 - CODE 36, OPTI-SPARK HIGH RESOLUTION PULSE
Ignition system supplies 2 timing inputs to PCM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (8 pulses per camshaft revolution). PCM can determine if either timing input is not being received by comparing inputs. If PCM detects low resolution pulse without detecting high pulse, Code 36 will set. Reference signal on resolution line toggles between zero and 5 volts as camshaft turns.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code will set if less than 60 high resolution timing pulses occur between each low resolution pulse and failure occurs 5 consecutive times.
- This step determines if PCM is sending out a signal to distributor for processing. If this signal is not available or is shorted to ground or voltage, distributor cannot ground it to produce reference pulses.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
An open, a short to voltage, a short to ground or a defective sensor inside distributor can prevent reference voltage from pulsing at PCM resolution terminal. If Code 36 is present and vehicle still does not start, check for Code 16 and use that chart first. If vehicle still will not start, go to NO START - ENGINE CRANKS OKAY in the BASIC TESTING article in this section.
Buick Roadmaster Estate Wagon 1994 - CODE 37, TCC BRAKE SWITCH ERROR
PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for voltage at brake switch.
- Simulates brake switch closed or brakes off.
- Checks TCC brake switch circuit between PCM and switch.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Code 37 can be caused by a misadjusted brake switch or a poor connection. Code may also be set by unusual driving habits i.e. stop-and-go expressway driving.
Buick Roadmaster Estate Wagon 1994 - CODE 38, TCC BRAKE SWITCH ERROR
PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for voltage at brake switch.
- Simulates brake switch closed or brakes off. Checks TCC brake switch circuit between PCM and switch.
- Checks circuit between TCC brake switch and PCM. Test opens TCC brake switch, simulating brakes applied.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Code may also be set by unusual driving habits i.e. stop-and-go expressway driving.
Buick Roadmaster Estate Wagon 1994 - CODE 41, OPTI-SPARK IGNITION SYSTEM OPEN OR SHORTED EST CKT
Ignition system provides 2 timing inputs to PCM, high resolution (360 pulses per camshaft revolution) and low resolution (4 pulses per crankshaft revolution). PCM uses these 2 inputs to determine individual spark timing for each cylinder. Once PCM calculates ignition timing, timing signal will be sent to ignition coil driver on EST circuit. Each timing pulse received by ignition coil driver will trigger coil driver to operate ignition coil. EST signal voltage ranges from about .5 volt to 4.5 volts. If a Code 41 is set, PCM will disable fuel injectors to prevent flooding of engine.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Determines if code is intermittent.
- This step determines if EST signal from PCM is available at ignition coil driver. EST circuit voltage should be between about .5 volt and 4.5 volts.
- Remaining steps ensure coil driver circuitry is okay. If all wiring and connections are okay, check ignition coil and ignition coil voltage supply.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Because coil driver gets its power from coil, check ignition feed circuit to ignition coil for opens.
Buick Roadmaster Estate Wagon 1994 - CODE 42, IC CIRCUIT GROUNDED
Ignition system provides 2 timing inputs to PCM, high resolution (360 pulses per camshaft revolution) and low resolution (4 pulses per crankshaft revolution). PCM uses these 2 inputs to determine individual spark timing for each cylinder. Once PCM calculates ignition timing, timing signal will be sent to ignition coil driver on EST circuit. Each timing pulse received by ignition coil driver will trigger coil driver to operate ignition coil. EST signal voltage ranges from about .5 volt to 4.5 volts.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If engine starts, code is intermittent.
- This test checks for an EST signal from PCM to ignition coil driver.
- Remaining tests check driver circuitry. Because coil driver gets its power from coil, check ignition coil feed circuit to ignition coil for opens.
Buick Roadmaster Estate Wagon 1994 - CODE 43, KNOCK SENSOR CIRCUIT
The knock sensor informs the PCM of engine detonation. The PCM will retard ignition timing based on signals from the knock sensors. Knock sensors produce an AC voltage signal which is proportional to the amount of engine detonation (knock). Internal sensor circuitry causes the 5-volt DC reference signal sent by the PCM to be pulled low to about 1.5 volts. Any AC voltage produced by the sensors will travel to the PCM on this same reference line. Code 43 will set if: one sensor circuit becomes open, resulting in a 2.2 to 4.1-volt reference being monitored by the PCM, both sensor circuits become open, resulting in a reference voltage greater than 4.1 volts being seen by the PCM, or one or both circuits become grounded, resulting in a low (less than .78 volt) reference voltage being seen by PCM.
If an audible knock is heard from the engine, repair the internal engine problem, as normally no knock should be detected at idle. The PCM supplies 5 volts on the knock sensor circuit which should be present at the knock sensor terminals when the sensors are disconnected.
If knock sensor circuit is shorted to voltage, Code 43 will set. With both sensors and PCM disconnected, no voltage should be present. An improperly installed sensor can prevent the knock sensor from grounding to the block.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
The PCM has the ability to diagnose opens and shorts on the knock sensor circuit. The scan tester will display if one or both sensors are open, or if both are grounded. Also, ensure knock sensor module is properly installed.
Buick Roadmaster Estate Wagon 1994 - CODE 44, LEFT HEATED OXYGEN SENSOR CIRCUIT LEAN INDICATION
NOTE: Engines are equipped with 2 oxygen sensors. On these models, Code 44 will set if the left sensor circuit is lean. Code 64 will set if the right sensor circuit is lean.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation.
NOTE: Test number refers to number on diagnostic chart.
- Checks to see if O2 sensor is registering a lean condition. Code 44 is set when O2 sensor voltage signal at control module is low (less than .3 volt) for a precalibrated period and system is operating in "closed loop".
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a Code 44 exist, block learn value will be about 150.
Buick Roadmaster Estate Wagon 1994 - O2 Sensor Wire
O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.
Buick Roadmaster Estate Wagon 1994 - Fuel Contamination
Water, even small amounts, near in-tank fuel pump inlet can be delivered to injector. Water may cause a lean exhaust and set Code 44.
Buick Roadmaster Estate Wagon 1994 - Fuel Pressure
System will be lean if fuel pressure is low. If necessary, monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING article in this section.
Buick Roadmaster Estate Wagon 1994 - Exhaust Leaks
If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition.
Buick Roadmaster Estate Wagon 1994 - Misfire Or Stall
If engine misfires or stalls (including running out of fuel) while vehicle is moving, a Code 44 may set. If Code 44 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 CODE 44 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Left O2 Signal C20 Purple/White Left O2 Ground C19 Tan/White
Fig. 55: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 44 Flow Chart
Buick Roadmaster Estate Wagon 1994 - CODE 45, LEFT HEATED OXYGEN SENSOR CIRCUIT RICH INDICATION
NOTE: Engines are equipped with 2 oxygen sensors. On these models, Code 45 will set if the left sensor circuit is rich. Code 65 will set if the right sensor circuit is lean.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation.
Code 45 indicates a rich exhaust. Diagnosis should begin with fuel pressure, leaking injector, HEI shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.
NOTE: Test number refers to number on diagnostic chart.
- Test checks to see if O2 sensor is registering a rich condition. Code 45 is set when vehicle is at operating temperature (in "closed loop"), throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period and time since engine start is one minute or more.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If other codes of lower number are set with Code 45, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a Code 45 to set. If other codes are not set, Code 45, rich exhaust, is most likely caused by:
Buick Roadmaster Estate Wagon 1994 - Fuel Pressure High
If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING article in this section. Control module can compensate for slight increases, but a Code 45 will be set if air/fuel ratio becomes too rich.
Buick Roadmaster Estate Wagon 1994 - Ignition Ground
If an open occurs on HEI ground circuit, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by control module on reference line of EST harness. Additional pulses result in a higher than actual engine speed signal. Control module will increase injector pulse width ("on" time) to match increased RPM signal. Scan tester will show higher than actual RPM, which can help in diagnosing this problem.
Buick Roadmaster Estate Wagon 1994 - Evaporative Fuel Canister
Fuel saturation of charcoal canister will cause a rich air/fuel ratio. If canister is full of fuel, check canister control valves and hoses.
Buick Roadmaster Estate Wagon 1994 - MAP Sensor
An output causing control module to sense a higher than normal manifold pressure (low vacuum) can cause system to go rich. Disconnecting MAP sensor will allow control module to substitute a fixed value for MAP sensor. If condition disappears, substitute a different MAP sensor, and continue testing.
Buick Roadmaster Estate Wagon 1994 - TPS
An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.
Buick Roadmaster Estate Wagon 1994 - O2 Sensor Contamination
O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White powdery coating to cover exterior of O2 sensor. False high signal voltage (low oxygen content sensed) produced is interpreted by control module as a rich mixture, causing control module to set Code 45.
Buick Roadmaster Estate Wagon 1994 - EGR Problem
EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling. Also check for shorted or leaking injector and fuel-contaminated oil. If Code 45 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 CODE 45 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Left O2 Signal C20 Purple/White Left O2 Ground C19 Tan/White
Buick Roadmaster Estate Wagon 1994 - CODE 46, PASS-KEY CIRCUIT
The PASS-Key system is designated to disable vehicle operation if the incorrect key or starting procedure is used. PASS-Key decoder module sends a signal to the PCM if the correct key is being used. If the proper signal does not reach the PCM, the PCM will not pulse the injectors, thus not allowing the vehicle to start. Code 46 will set if proper signal is not being received on fuel enable signal circuit to PCM when ignition is turned on.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If engine cranks but does not start, it indicates the portion of the module which generates the signal to the PCM is not operating or fuel enable signal circuit is open or shorted to ground. If decoder module is found to be okay, PCM may be at faulty, but this not a likely condition.
- If Code 46 is stored and engine will not crank, it indicates that there is a Pass-Key problem or incorrect key or starting procedure is being used.
Buick Roadmaster Estate Wagon 1994 - CODE 46, PASS-KEY DIAGNOSIS
NOTE: For complete system diagnosis, see ANTI-THEFT SYSTEM article in the ACCESSORIES/SAFETY EQUIPMENT section.
PASS-Key is a sophisticated system that interfaces PCM and starter with a power source, decoder module, starter enable relay, ignition switch and instrument cluster. Check system for following common problems:
- Ensure ignition key resistor pellet is not cracked, dirty or coated. Ensure excess plastic does not exist around pellet contacts.
- Check ignition key pellet sensing contacts in ignition lock cylinder. Look into cylinder lock. If contacts are damaged or are not Silver in color, replace cylinder lock.
- Check related fuses.
- Check security indicator bulb in the instrument panel.
A defective resistor pellet within ignition key or incorrect resistance value of key (15 different assigned values) will prevent vehicle from starting. Key must be correct electrically and mechanically. If incorrect key is used to try to start vehicle, decoder will not allow vehicle to start for 2-4 minutes, even after correct key is inserted.
If starter enable relay must be replaced, check circuit to starter solenoid for possible short. A short may have caused relay to fail.
Buick Roadmaster Estate Wagon 1994 - CODE 47, KNOCK SENSOR MODULE
Knock sensor module is located inside PCM.
Buick Roadmaster Estate Wagon 1994 - CODE 48, MASS AIRFLOW SENSOR
Mass airflow meter measures amount of induction airflow. This information is used by PCM to determine adjustments to air/fuel ratio. MAF sensor is a hot-wire type. Sensor maintains hot wire at a predetermined temperature. The greater the airflow across the hot wire, the more current is required to maintain hot wire temperature. Sensor changes the current requirements into a frequency signal which is read by the PCM. The PCM calculates airflow based upon this signal.
NOTE: Test numbers refer to numbers on diagnostic charts.
- Determines if fault is a hard failure or an intermittent condition.
- Checks for 5-volt reference from PCM.
- Verifies both ignition voltage and a good ground circuit are available.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation or a broken wire inside insulation. Code 48 could be caused by a vacuum leak. Check short and long term fuel trim for being in optimum range (both banks).
Buick Roadmaster Estate Wagon 1994 - CODE 50, SYSTEM VOLTAGE LOW
PCM monitors voltage on ignition feed circuit (Pink wire). Normal voltage is 9.6-16 volts. If voltage drops below 8 volts, Code 50 will set and Malfunction Indicator Light (MIL) will illuminate.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
An open in ignition feed circuit (Pink wire) or extremely low voltage may cause loss of serial data, no start condition and malfunction of the MIL. Additional codes may be set.
Buick Roadmaster Estate Wagon 1994 - CODE 51, FAULTY PROM/MEM-CAL
Ensure all pins are fully inserted in socket. If pins are okay, replace PROM/MEM-CAL, clear memory and recheck. If Code 51 reappears, replace control module.
Buick Roadmaster Estate Wagon 1994 - CODE 53, SYSTEM VOLTAGE HIGH
This code indicates a basic charging system problem. Code 53 will set when voltage at control module terminal is greater or less than specification for a precalibrated time. If voltage at PCM battery voltage terminal is not within specification, check and repair charging system.
Buick Roadmaster Estate Wagon 1994 CHARGING SYSTEM SPECIFICATIONS
Application Minimum Charge Maximum Charge 5.7L 9.6 16.0
Buick Roadmaster Estate Wagon 1994 - CODE 55, PCM ERROR
Ensure PCM grounds are okay. Ensure correct EPROM is being used and that it is properly installed. If okay, replace PCM. Clear codes, confirm closed loop operation and check operation of Malfunction Indicator Light (MIL).
Buick Roadmaster Estate Wagon 1994 - CODE 55, FUEL LEAN MONITOR
PCM is capable of determining if fuel system can deliver adequate fuel during power enrichment (heavy acceleration). During power enrichment conditions, PCM expects to see both O2 sensors registering rich. If both sensors do not register rich, Code 55 will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 55 will set if PCM detects lean O2 sensor voltage for 8 seconds during power enrichment. This checks for proper fuel pressure.
- Restricting the fuel line allows fuel pressure to build to greater than regulated pressure (greater than 47 psi). DO NOT allow pressure to exceed 60 psi.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
A plugged fuel filter or restricted fuel line can prevent adequate fuel from being supplied during power enrichment. Vapor lock can also cause Code 55.
Fig. 67: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 55 Flow Chart
Buick Roadmaster Estate Wagon 1994 - CODE 58, TRANSMISSION TEMPERATURE SENSOR HIGH TEMPERATURE
Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when trans fluid is cold and as fluid warms voltage signal will drop. A very low signal voltage indicates a high fluid temperature or a failure in sensor circuit. Normal fluid temperature range is between 167?F-212?F (75?C-100?C).
Code 58 will set when sensor indicates a temperature of 148?C or greater for 5 seconds. Malfunction Indicator Light (MIL) will illuminate and PCM will use a default sensor value of 90?C.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for a short to ground or an out-of-calibration sensor.
- Checks for an internal fault within the transmission by creating an open.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check harness routing for a potential short to ground in signal circuit. Temperature should rise steadily to approximately 85?C then stabilize. A skewed sensor could result in delayed shifts or TCC enabled complaints.
Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.
Buick Roadmaster Estate Wagon 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 59, TRANSMISSION TEMPERATURE SENSOR LOW TEMPERATURE
Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when trans fluid is cold and as fluid warms voltage signal will drop. A very high signal voltage indicates a low fluid temperature or a failure in sensor circuit. Normal fluid temperature range is between 167?F-212?F (75?C-100?C).
Code 59 will set when sensor indicates a temperature of less than -40?C for 5 seconds. Malfunction Indicator Light (MIL) will not illuminate and PCM will use a default sensor value of 90?C.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This test determines if a current condition exists.
- Simulates a Code 58. If PCM recognizes low signal voltage, and scan displays 146 degrees centigrade or higher, PCM and wiring are okay.
- Checks if signal circuit is open. Five volts should be present at sensor connector.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Temperature should rise steadily to approximately 212 ?F (90?C) then stabilize. A faulty connection or an open in ground or signal circuit can result in Code 59. A skewed sensor could result in firm shifts or TCC enabled complaints.
Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.
Buick Roadmaster Estate Wagon 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Fig. 72: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 59 Flow Chart
Buick Roadmaster Estate Wagon 1994 - CODE 63, OPEN RIGHT HEATED OXYGEN SENSOR CIRCUIT
NOTE: Engine is equipped with 2 oxygen sensors. On this model, code will set if the right sensor circuit is open. Code 13 will set if the left sensor circuit is open. Oxygen sensors use a heating element. Heating element is not controlled by PCM.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This tests if problem still exists. Vehicle cannot enter "closed loop" mode if oxygen sensor circuit is open. Code indicates an open in O2 sensor circuit. Code will set if Engine is at normal operating temperature, neither Code 21 nor Code 22 is stored, oxygen sensor voltage is constant within a specified range (.34-.55 volt), throttle angle is greater than idle, a precalibrated amount of time has elapsed since start-up and all conditions have existed for a precalibrated amount of time.
- Determines if oxygen sensor, wiring or control module is at fault. If wiring is good, grounding oxygen sensor wire will cause .45 volt reference supplied by control module to pull low.
- This tests oxygen sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Control module will not go into closed loop if code is set. Code may set if vehicle runs out of fuel or stalls while vehicle is in motion. If oxygen sensor ground becomes loose, a false oxygen sensor reading will occur. This can result in a Code 63 being set. On models equipped with an oxygen sensor heating element, element resistance should be 3.5-14 ohms.
Buick Roadmaster Estate Wagon 1994 CODE 63 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Right O2 Signal C8 Purple Right O2 Ground C7 Tan
Buick Roadmaster Estate Wagon 1994 - CODE 64, RIGHT HEATED OXYGEN SENSOR LEAN INDICATION
NOTE: Engines are equipped with 2 oxygen sensors. On these models, Code 64 will set if the right sensor circuit is lean. Code 44 will set if the left sensor circuit is lean.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation.
NOTE: Test number refers to number on diagnostic chart.
- Checks to see if O2 sensor is registering a lean condition. Code 64 is set when O2 sensor voltage signal at control module is low (less than .3 volt) for a precalibrated period and system is operating in "closed loop".
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a Code 64 exist, block learn value will be about 150.
Buick Roadmaster Estate Wagon 1994 - O2 Sensor Wire
O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.
Buick Roadmaster Estate Wagon 1994 - Fuel Contamination
Water, even small amounts, near in-tank fuel pump inlet can be delivered to injector. Water may cause a lean exhaust and set Code 64.
Buick Roadmaster Estate Wagon 1994 - Fuel Pressure
System will be lean if fuel pressure is low. If necessary, monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING article in this section.
Buick Roadmaster Estate Wagon 1994 - Exhaust Leaks
If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition.
Buick Roadmaster Estate Wagon 1994 - Misfire Or Stall
If engine misfires or stalls (including running out of fuel) while vehicle is moving, a Code 64 may set. If Code 64 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 CODE 64 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Right O2 Signal C8 Purple Right O2 Ground C7 Tan
Fig. 77: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 64 Flow Chart
Buick Roadmaster Estate Wagon 1994 - CODE 65, RIGHT HEATED OXYGEN SENSOR RICH INDICATION
NOTE: Engines are equipped with 2 oxygen sensors. On these models, Code 65 will set if the right sensor circuit is rich. Code 45 will set if the left sensor circuit is lean.
O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600?F (316?C). An open sensor circuit or cold sensor causes "open loop" operation.
Code 65 indicates a rich exhaust. Diagnosis should begin with fuel pressure, leaking injector, HEI shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.
NOTE: Test number refers to number on diagnostic chart.
- Test checks to see if O2 sensor is registering a rich condition. Code 65 is set when vehicle is at operating temperature (in "closed loop"), throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period and time since engine start is one minute or more.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If other codes of lower number are set with Code 65, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a Code 65 to set. If other codes are not set, Code 65, rich exhaust, is most likely caused by:
Buick Roadmaster Estate Wagon 1994 - Fuel Pressure High
If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING article in this section. Control module can compensate for slight increases, but a Code 45 will be set if air/fuel ratio becomes too rich.
Buick Roadmaster Estate Wagon 1994 - Ignition Ground
If an open occurs on HEI ground circuit, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by control module on reference line of EST harness. Additional pulses result in a higher than actual engine speed signal. Control module will increase injector pulse width ("on" time) to match increased RPM signal. Scan tester will show higher than actual RPM, which can help in diagnosing this problem.
Buick Roadmaster Estate Wagon 1994 - Evaporative Fuel Canister
Fuel saturation of charcoal canister will cause a rich air/fuel ratio. If canister is full of fuel, check canister control valves and hoses.
Buick Roadmaster Estate Wagon 1994 - MAP Sensor
An output causing control module to sense a higher than normal manifold pressure (low vacuum) can cause system to go rich. Disconnecting MAP sensor will allow control module to substitute a fixed value for MAP sensor. If condition disappears, substitute a different MAP sensor, and continue testing.
Buick Roadmaster Estate Wagon 1994 - TPS
An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.
Buick Roadmaster Estate Wagon 1994 - O2 Sensor Contamination
O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White powdery coating to cover exterior of O2 sensor. False high signal voltage (low oxygen content sensed) produced is interpreted by control module as a rich mixture, causing control module to set Code 65.
Buick Roadmaster Estate Wagon 1994 - EGR Problem
EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling. Also check for shorted or leaking injector and fuel-contaminated oil. If Code 65 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.
Buick Roadmaster Estate Wagon 1994 CODE 65 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application PCM Terminal Wire Color Right O2 Signal C8 Purple Right O2 Ground C7 Tan
Buick Roadmaster Estate Wagon 1994 - CODE 66, A/C PRESSURE SENSOR
A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. PCM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from PCM and returns an input signal to PCM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.6 volts.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks voltage signal from A/C pressure sensor to PCM.
- Checks to see if high signal is from a shorted sensor or a short to voltage in circuit. Normally, disconnecting sensor would make a normal circuit go to nearly zero volts.
- Checks to see if low voltage signal is from sensor or circuit. Jumpering sensor signal circuit to 5-volt reference checks circuit, connections and PCM.
- Checks to see if low voltage signal was due to an open in sensor circuit; previous step eliminated pressure sensor as a possible cause.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Code 66 sets when signal voltage falls outside normal sensor range and is not due to a A/C system problem. If problem is intermittent, check for opens or shorts in harness and poor connections. If wiring is okay, replace pressure sensor. If code resets, replace PCM.
Buick Roadmaster Estate Wagon 1994 - CODE 67, A/C PRESSURE SENSOR
PCM determines when A/C clutch is engaged by monitoring A/C status line. If A/C pressure does not increase by at least 4 psi when A/C clutch is turned on, Code 67 will set.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 67 will set if PCM does not detect a A/C pressure change when A/C clutch has been cycled.
- If relay power feed is intermittent, A/C clutch status terminal may not detect voltage when A/C is commanded on.
- Check A/M electrical harness for problems. If A/C clutch status line becomes intermittently open or shorted while compressor is on, PCM will be wrongly detecting A/C clutch going on and off. When this occurs and clutch remains engaged, PCM will not detect pressure change and a Code 67 will be set.
- If A/C compressor clutch status circuit is intermittently open or shorted while compressor is on, PCM will wrongly detect compressor cycling on and off, but PCM will detect no pressure change and a Code 67 will set.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
A Code 67 will store in PCM memory but will not turn on the SERVICE ENGINE SOON light. An A/C system low on charge could cause a Code 67 to set.
Buick Roadmaster Estate Wagon 1994 - CODE 68, A/C RELAY CIRCUIT SHORTED
When PCM detects A/C has been requested, PCM will activate A/C clutch relay. When relay is activated, voltage should be present at both A/C compressor clutch and A/C clutch status terminal at PCM. If PCM detects voltage on A/C status line when A/C has not been commanded on, Code 68 will set. A short to voltage anywhere on A/C status line, or stuck relay contacts, will set Code 68. When Code 68 is set, PCM does not turn on SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 68 sets if voltage is detected on A/C status line for more than 20 seconds after PCM has disengaged A/C relay.
- This step will isolate ignition feed portion of circuit from clutch circuit.
- If Code 68 reappears at this step, PCM is internally shorted to voltage.
Buick Roadmaster Estate Wagon 1994 - CODE 69, A/C COMPRESSOR RELAY
When PCM detects A/C has been requested, PCM will activate the A/C clutch relay. When the relay has been activated, voltage should be present at both the A/C compressor clutch and the A/C clutch status line terminal of the PCM. If the PCM activates the A/C clutch relay but does not detect voltage present at the A/C status terminal for more than 10 seconds, Code 69 will set. An open or short to ground at any point in the A/C status circuit will cause Code 69 to set. A Code 69 fault will be stored in PCM memory but will not turn on the SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 69 will set if the PCM has commanded the A/C on and no voltage is detected on the A/C status line after 20 seconds.
- If the A/C compressor clutch operates properly and scan tester indicates A/C status off, then an open exists between the PCM and the splice to the compressor.
Buick Roadmaster Estate Wagon 1994 - CODE 70, A/C COMPRESSOR RELAY DRIVER
Relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech-1 will enable circuit for 5 seconds.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 72, VSS
Speed sensor is a PM generator located on transmission output shaft.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Disable TC system (if equipped) when performing this step. Whenever ignition is cycled off and then back on, TC system will default on.
- An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals. Prior to replacing PCM check for updated software for PCM (reprogrammable).
- Ensure harness is not routed too close to hot exhaust components.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Code 24 will set if vehicle speed is not detected at start off. Code 72 will set when vehicle speed has been detected and then lost.
Fig. 90: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 72 Schematic (5.7L) VSS
Fig. 91: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 72 Flow Chart (5.7L) VSS
Buick Roadmaster Estate Wagon 1994 - CODE 73, PRESSURE CONTROL SOLENOID
Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM compares TPS voltage, engine RPM and other inputs to determine proper line pressure for a given load. PCM regulates pressure by applying a varying amperage to pressure control solenoid. Amperage varies from 0.1 to 1.1 amps.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks ability of the PCM to command pressure control solenoid.
- Checks for voltage at PCM.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check for poor connections at PCM and at transmission connector.
Buick Roadmaster Estate Wagon 1994 - CODE 75, TRANSMISSION VOLTAGE LOW
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for normal battery voltage of 9-15 volts.
- Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.
Buick Roadmaster Estate Wagon 1994 - CODE 77, PRIMARY COOLING FAN DRIVER
Cooling fan relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech-1 will enable circuit for 5 seconds.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Fig. 97: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 77 Flow Chart
Buick Roadmaster Estate Wagon 1994 - CODE 78, SECONDARY COOLING FAN DRIVER
Cooling fan relay is supplied voltage when ignition is on. PCM controls solenoid valve by providing a ground through one of its Quad-Drivers Modules (QDM). When relay is actuated, terminal is grounded and its monitored voltage will be low. When an output is off, its terminal voltage will be high. Each QDM has a separate fault line to indicate presence of a current fault to control module central processor.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech-1 will enable circuit for 5 seconds.
- This check can detect a partially shorted coil which would cause excessive current flow. Excessive current flow to a QDM will be detected as a fault and set a code.
- The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 79, TRANSMISSION FLUID OVERTEMP
PCM supplies and monitors a 5-volt reference to sensor. As transmission temperature changes, sensor resistance changes, affecting monitored voltage. When fluid is cold, resistance is high, resulting in a high monitored voltage.When fluid is hot, resistance is low, resulting in a low monitored voltage.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for out-of-calibration sensor or shorted circuit.
- Simulates Code 59.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
See Code 59 chart to check transmission temperature sensor temperature-to-resistance values. Also, check transmission fluid level.
Buick Roadmaster Estate Wagon 1994 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 212 (100) 177 194 (90) 241 158 (70) 467 104 (40) 1459 68 (20) 3520 23 (-5) 12,300 14 (-10) 16,180 0 (-18) 25,000 -4 (-20) 28,680 -22 (-30) 52,700 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Roadmaster Estate Wagon 1994 - CODE 80, TRANSMISSION COMPONENT SLIPPING
PCM monitors difference between engine speed and transmission input shaft speed. With selector in D3 or D4 (indicated gear 2, 3 or 4), and TCC is locked, scan should display engine speed closely matching input speed.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks indicated range signal to the actual selected range.
- Checks torque converter for slippage while in a commanded locked-up state.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check for poor connections at pass-through connector. A faulty transmission range pressure switch assembly may set Code 80.
Buick Roadmaster Estate Wagon 1994 - CODE 81, 2-3 SHIFT SOLENOID
Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks 2-3 shift solenoid and internal transmission for shorts.
- Checks for power to 2-3 shift solenoid from ignition through the fuse.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.
Buick Roadmaster Estate Wagon 1994 - CODE 82, 1-2 SHIFT SOLENOID
Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit for solenoid.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks 1-2 shift solenoid and internal transmission for shorts.
- Checks for power to 1-2 shift solenoid from ignition through the fuse.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.
Buick Roadmaster Estate Wagon 1994 - CODE 84, 3-2 CONTROL SOLENOID - A/T
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks 3-2 shift solenoid and internal transmission for shorts.
- Checks for power to 3-2 shift solenoid from ignition through the fuse.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.
Fig. 110: Buick Roadmaster Estate Wagon 1994 - Component Locations - Code 84 Flow Chart
Buick Roadmaster Estate Wagon 1994 - CODE 85, TCC STUCK ON
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks mechanical state of TCC when PCM commands TCC solenoid off. TCC slip speed should increase.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied, and D2 is selected, TCC fluid will mechanically apply the TCC, causing an engine stall.
Buick Roadmaster Estate Wagon 1994 - CODE 90, TCC SOLENOID CIRCUIT
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks for a shorted internal transmission harness or TCC solenoid.
- Checks power supply to TCC solenoid.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Check all connections to transmission pass-through connector. An open in the ignition feed circuit will cause multiple codes to set.
Buick Roadmaster Estate Wagon 1994 - CODE 95, CHANGE OIL LIGHT
PCM monitors driving conditions and determines when to turn on change oil light. Maximum possible mileage accumulation is 7500 miles; however, PCM may turn on light sooner depending upon driving conditions (i.e. temperature and engine load history). Code will set and PCM will turn on light if wrong monitored voltage is present on light circuit for 26 seconds or more. PCM will not turn on SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Unplugging PCM will determine if circuit is shorted to ground or if the PCM is at fault.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
To reset oil light, turn ignition on with off. Cycle accelerator pedal from closed throttle to wide open throttle 3 times within 5 seconds. If light will not reset, monitor throttle angle and ensure angle changes from less than 7.5 percent to greater than 75 percent.
Buick Roadmaster Estate Wagon 1994 - CODE 96, LOW OIL LIGHT
Code will set and PCM will turn on light if wrong monitored voltage is present on light circuit for 26 seconds or more. PCM will not turn on SERVICE ENGINE SOON light.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Unplugging PCM will determine if circuit is shorted to ground or if the PCM is at fault.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Inspect harness and all related connections, including PCM connections. These may cause an intermittent code to set.
Buick Roadmaster Estate Wagon 1994 - CODE 97, VSS OUTPUT CIRCUIT
NOTE: Test numbers refer to numbers on diagnostic chart.
- Disable Traction Control (TC) system (if equipped) prior to this step. Switch is located in glove box. Whenever ignition is cycled off and then on, TC system will default to on. If vehicle speed is indicated at this point, code is intermittent.
- Use Jumper Harness (J 35616-A) to prevent damage to harness.
Buick Roadmaster Estate Wagon 1994 - Diagnostic Aids
Inspect harness and all related connections, including PCM connections.
Buick Roadmaster Estate Wagon 1994 - SUMMARY
If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.