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Buick Skylark Custom 1993 - G - TESTS W/CODES - 2.3L 1993 ENGINE PERFORMANCE General Motors Self-Diagnostics - 2.3L 4 Cyl. ECM/PCM
Buick Skylark Custom 1993 - 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 Skylark Custom 1993 - SELF-DIAGNOSTIC SYSTEM OVERVIEW
NOTE: Electronic Control Module (ECM) may also be referred to as Powertrain Control Module (PCM) 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 may 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 BASIC TESTING article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.
- If no trouble codes were displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will identify proper system or component to check in I - SYS/COMP TESTS 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 Skylark Custom 1993 - RETRIEVING CODES (NON-SCAN)
NOTE: Inserting jumper wire into test and ground terminals of ALDL connector 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 this section.
- Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector attached to control module wiring harness. Most ALDL connectors are located under dash on driver side of vehicle. For exact location of ALDL, see COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of ALDL connector. 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 ALDL connector.
Fig. 1: Buick Skylark Custom 1993 - Component Locations - ALDL Connector Terminal ID
Buick Skylark Custom 1993 - 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" of ALDL 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 ALDL 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 Skylark Custom 1993 - TROUBLE CODE DEFINITION
Buick Skylark Custom 1993 ECM/PCM TROUBLE CODE DEFINITION
Code No. Circuit Affected 12 (1) No RPM Reference Pulse 13 Oxygen Sensor Circuit Open 14 Coolant Temperature Sensor Signal Voltage Low 15 Coolant Temperature Sensor Signal Voltage High 16 Loss Of 2X Signal (2.3L) 19 Intermittent 7X Signal (2.3L) 21 TPS Signal Voltage High 22 TPS Signal Voltage Low 23 MAT Sensor Signal Voltage High 24 Vehicle Speed Sensor 25 MAT Sensor Signal Voltage Low 26 Quad-Driver Error (2.3L) 27 Or 28 Quad-Driver Error (2.3L) 32 EGR System Error 33 MAP Sensor Signal Voltage High 34 MAP Sensor Signal Voltage Low 35 IAC Idle Speed Error 41 1X Reference Circuit (2.3L) 42 EST Circuit Open Or Grounded 43 Knock Sensor Error 44 Lean Exhaust Indication 45 Rich Exhaust Indication 51 Faulty PROM, MEM-CAL Or ECM/PCM 52 Faulty/Missing CAL-PAC Or MEM-CAL 53 System Overvoltage 54 Fuel Pump Voltage Low 55 ECM/PCM Error 65 Injector Current Low (2.3L) 66 A/C Pressure Sensor 85 PROM Error 87 EEPROM Error
(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). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime control module-related Codes 51, 52 or 55 are displayed with another code, start with 50-series code, and then proceed to lower numbered codes.
Buick Skylark Custom 1993 - 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:
- Manually 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, manually enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Codes 13, 15, 24, 44 and 45 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 Skylark Custom 1993 - CLEARING TROUBLE CODES
Turn ignition switch to ON position, and ground diagnostic test terminal "B" at ALDL connector. 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 removed, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.
Buick Skylark Custom 1993 - 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. On Lumina, control module is located on right side of engine compartment. See COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section.
Buick Skylark Custom 1993 - 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 Skylark Custom 1993 - Field Service Mode Check
If ALDL 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. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
Buick Skylark Custom 1993 - SPECIAL TOOLS (DIAGNOSTIC)
NOTE: A scan tester plugged into ALDL may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M" on P-4 systems). 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 Skylark Custom 1993 - 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 ALDL, 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.
NOTE: Code 12 should always exist when ALDL 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 specification will not set a trouble code but will cause driveability problems.
Using scan tester is 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 ALDL test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by scan tester.
Buick Skylark Custom 1993 - 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 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 Skylark Custom 1993 SCAN DATA - PORT FUEL INJECTION (1)
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 Counts 118 - 138 (128 Normal) Canister Purge Sol On/Off On/Engine Cold (Idle Some) Clear Flood On/Off **See Scan Tester Manual** Coolant Fan On/Off Off Below 216?F (102?C) Coolant Temp. ?C 85-115? (Norm. Temperature) 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 5-60 Ignition/Crank On/Off On With Ignition/Crank Injector Pulse Width Mil./Sec 1-4 And Varying INT (Integrator) Counts 110-145 (128 Normal) Knock Retard (ESC) Counts 0 - 255 Knock Signal Yes/No Yes When Knock Exists MAT ?C 10 - 90? MAP Volts 1.0 (Idle) to 3 (WOT) "Open/Closed Loop Status" Ol/Cl Closed/Open During Extended Idle O2 Sensor Millivolts 1 (Lean) To 1000 (Rich) P/N Switch P/N/RDL Park/Neutral P/S Switch Norm/Hi Normal PROM I.D. PROM No. 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) TPS Volts .2-.9 (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 Water Injection On/Off On When Injecting 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
(1) Values have been updated per TSB 93-6-21, dated December 16, 1992.
Buick Skylark Custom 1993 - ECM/PCM CODE CHARTS
NOTE: In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp.
Buick Skylark Custom 1993 - CODE 13 - OPEN OXYGEN SENSOR CIRCUIT
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 13 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 Skylark Custom 1993 - Diagnostic Aids
Control module will not go into closed loop if Code 13 is set. Code 13 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 Skylark Custom 1993 CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body O2 Signal A12 Black O2 Ground B6 Tan 2.3L "N" Body O2 Signal A12 Purple O2 Ground B6 Tan
Buick Skylark Custom 1993 - CODE 14 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE LOW)
NOTE: This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.
- Code 14 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 14 still exist.
- This tests for grounded sensor signal line between control module and coolant sensor.
Buick Skylark Custom 1993 - 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 14 is set, control module will turn on electric cooling fan(s) if equipped.
Buick Skylark Custom 1993 CODE 14 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body CTS Signal C10 Yellow CTS Ground B2 Purple 2.3L "N" Body CTS Signal C10 Yellow CTS Ground B2 Black
Buick Skylark Custom 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Skylark Custom 1993 - CODE 15 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- Code 15 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 15 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 Skylark Custom 1993 - 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 14 is set, control module will turn on electric cooling fan(s) if equipped.
Buick Skylark Custom 1993 CODE 15 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body CTS Signal C10 Yellow CTS Ground B2 Purple 2.3L "N" Body CTS Signal C10 Yellow CTS Ground B2 Black
Buick Skylark Custom 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Skylark Custom 1993 - CODE 16 - MISSING 2X REFERENCE CIRCUIT (2.3L)
Ignition module sends a reference signal to ECM twice per revolution to indicate crankshaft position and RPM so ECM can determine when to pulse ignition coils and control ignition timing. This signal is called "2X" reference because it occurs twice per crankshaft revolution. Ignition module applies 5 volts to 2X circuit, which is monitored by ECM. Ignition module toggles this signal to ground twice per crankshaft revolution. Code 16 will set if ECM detects 1X reference signals with no 2X pulses.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Determines if ECM recognizes a problem. Problem is intermittent and could be due to a loose connection if ECM does not set Code 16 at this point.
- This step simulates a 2X signal. ECM should recognize drop in voltage as test light probe is removed. This step will give accurate results only if proper sequence is used. Turn ignition off, turn ignition on, scan 2X reference while touching and removing test light connected to battery voltage to terminal "H" of ignition module harness.
- If ECM did not recognize simulation of 2X signal, circuit may be open or shorted to ground between ignition module harness connector and ECM. If circuit is okay, ECM is faulty.
- Step 2) indicated 2X reference circuit was okay and ECM is capable of recognizing a simulated 2X signal. This indicates either a poor connection or a faulty ignition module caused Code 16.
Buick Skylark Custom 1993 - Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside the insulation. Inspect ECM harness connector terminal and ignition module terminal for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire contact and damaged harness.
Buick Skylark Custom 1993 - CODE 19 - INTERMITTENT 7X SIGNAL (2.3L)
The ignition control module sends a reference signal to the ECM 7 times per crankshaft revolution to indicate crankshaft position and RPM so that the ECM can determine when to pulse the ignition coils and control ignition timing. A 5-volt reference is supplied to the ECM from terminal "G" of the ignition module. This 5-volt reference signal is monitored by the ECM. The ignition module pulls this signal low based upon 7X reference pulses. The seventh pulse is used for crankshaft position (sync) reference. Code 19 is set if the ECM misses at least 20 sync pulses within 4 minutes and 16 seconds.
- This step determines if the ECM recognizes a problem. If it doesn't set Code 19 at this point, the problem is intermittent.
- When a 7X resync occurs, engine stumble also occurs. If a component connection or circuitry is at fault, engine stumble may be induced by wiggling the circuit or connection.
Buick Skylark Custom 1993 - Diagnostic Aids
If vehicle has non-standard electrical equipment (CB radios, 2-way radios, etc.) check to see if their operation may be causing a 7X resync which may set Code 19. If a "cranks but won't start" condition has existed, code may be due to 20 attempted starts without turning off ignition switch.
Buick Skylark Custom 1993 - CODE 21 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE HIGH)
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 Skylark Custom 1993 - 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 Skylark Custom 1993 CODE 21 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body TPS Signal B7 Dark Blue TPS Ground B2 Purple TPS Reference A3 Gray 2.3L "N" Body TPS Signal B7 Dark Blue TPS Ground B2 Black TPS Reference A3 Gray
Buick Skylark Custom 1993 - CODE 22 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE LOW)
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 a Code 21. 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 Skylark Custom 1993 - 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 Skylark Custom 1993 CODE 22 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body TPS Signal B7 Dark Blue TPS Ground B2 Purple TPS Reference A3 Gray 2.3L "N" Body TPS Signal B7 Dark Blue TPS Ground B2 Black TPS Reference A3 Gray
Buick Skylark Custom 1993 - CODE 23 - MAT SENSOR (SIGNAL VOLTAGE HIGH)
NOTE: Test numbers refer to numbers on diagnostic chart.
- This checks if code is result of a hard failure or an intermittent condition. Code 23 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 a Code 25. 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 Skylark Custom 1993 - Diagnostic Aids
If engine is allowed to cool overnight, coolant and MAT sensor values should be close to each other when measured by scan tester. Code 23 will result if signal and ground circuits become open. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.
Buick Skylark Custom 1993 CODE 23 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body MAT Signal C9 Tan MAT Ground B1 Black 2.3L "N" Body MAT Signal C9 Tan MAT Ground B1 Black/Orange
Buick Skylark Custom 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Skylark Custom 1993 - 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 3 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 3 MPH.
- Before replacing control module, PROM/MEM-CAL should be checked for correct application.
Buick Skylark Custom 1993 - 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 Skylark Custom 1993 - CODE 25 - MAT SENSOR (SIGNAL VOLTAGE LOW)
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 MAT 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 Skylark Custom 1993 - Diagnostic Aids
If engine is allowed to cool overnight, coolant temperature sensor and MAT 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 Skylark Custom 1993 CODE 25 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body MAT Signal C9 Tan MAT Ground B1 Black 2.3L "N" Body MAT Signal C9 Tan MAT Ground B1 Black/Orange
Buick Skylark Custom 1993 TEMPERATURE-TO-RESISTANCE VALUES (1)
Temperature ?F (?C) Ohms 210 (100) 185 160 (70) 450 100 (38) 1800 70 (20) 3400 20 (-7) 13,500 0 (-18) 25,000 -40 (-40) 100,700
(1) Measure resistance across sensor terminals.
Buick Skylark Custom 1993 - CODE 26 - QUAD-DRIVER ERROR (2.3L)
ECM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.
QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.
Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault".
Buick Skylark Custom 1993 - CODE 27 - QUAD-DRIVER NO. 1 ERROR (2.3L "L" BODY)
ECM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.
QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.
Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault". Code 27 will set if QDM No. 1 is high for 20 seconds or more with battery voltage is sensed at greater than 10.5 volts.
Buick Skylark Custom 1993 - CODE 27 - QUAD-DRIVER NO. 1 ERROR (2.3L "N" BODY)
ECM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.
QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.
Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault". Because of the brake and 2nd gear switches in the TCC circuit, Code 27 will set if QDM No. 1 is high for 20 seconds or more with battery voltage is sensed at greater than 10.5 volts and TCC is commanded on.
Buick Skylark Custom 1993 - CODE 28 - QUAD-DRIVER NO. 2 ERROR (2.3L "L" BODY)
ECM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.
QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.
Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault". Code 28 will set if QDM No. 2 is high for 20 seconds or more with battery voltage is sensed at greater than 10.5 volts.
Buick Skylark Custom 1993 - CODE 28 - QUAD-DRIVER NO. 2 ERROR (2.3L "N" BODY)
ECM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.
QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.
Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault". Code 28 will set if QDM No. 2 is high for 20 seconds or more with battery voltage is sensed at greater than 10.5 volts.
Buick Skylark Custom 1993 - CODE 33 - MAP SENSOR (SIGNAL VOLTAGE HIGH)
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 Skylark Custom 1993 - 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 Skylark Custom 1993 CODE 33 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body MAP Signal D4 Light Green MAP Ground B1 Black MAP Reference A4 Gray 2.3L "N" Body MAP Signal D4 Light Green MAP Ground B1 Black/Orange MAP Reference A4 Gray
Buick Skylark Custom 1993 - CODE 34 - MAP SENSOR (SIGNAL VOLTAGE LOW)
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 Skylark Custom 1993 - 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 Skylark Custom 1993 CODE 34 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body MAP Signal D4 Light Green MAP Ground B1 Black MAP Reference A4 Gray 2.3L "N" Body MAP Signal D4 Light Green MAP Ground B1 Black/Orange MAP Reference A4 Gray
Buick Skylark Custom 1993 - CODE 35 - IAC IDLE SPEED ERROR WITHOUT TECH 1
Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- IAC driver is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body.
- Checks IAC movement quality from step 1). Between 700-1500 RPM, engine speed should change smoothly with each flash of tester light in both extend and retract. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
- Steps 1) and 2) verified proper IAC valve operation, while this step checks IAC circuits. Each light on node light should flash Red and Green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash Red and Green.
NOTE: For IAC reset procedure, see IDLE SPEED & MIXTURE in ADJUSTMENTS article in this section.
Buick Skylark Custom 1993 - Diagnostic Aids
A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. Scan counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC using driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.
Buick Skylark Custom 1993 - System Too Lean
If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. Scan tester and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mV (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mV (.8 volt). This may also set Code 45.
Buick Skylark Custom 1993 - System Too Rich
If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. System may be obviously rich, with Black smoke from exhaust pipe. Scan tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mV (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.
Buick Skylark Custom 1993 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Buick Skylark Custom 1993 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Buick Skylark Custom 1993 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Buick Skylark Custom 1993 - CODE 35 - IAC IDLE SPEED ERROR USING TECH I
Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Tech 1 RPM control mode is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
- This test uses Tech 1 to command IAC-controlled idle speed. Control module issues commands to obtain requested idle speed. Each light on node light should flash Red and Green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash Red and Green.
Buick Skylark Custom 1993 - Diagnostic Aids
A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. Scan counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC with driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.
Buick Skylark Custom 1993 - System Too Lean
If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. Scan and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mV (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mV (.8 volt). This may also set Code 45.
Buick Skylark Custom 1993 - System Too Rich
If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. System may be obviously rich, with Black smoke from exhaust pipe. Scan tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mV (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.
Buick Skylark Custom 1993 - Throttle Body
Remove IAC, and inspect bore for evidence of IAC valve dragging.
Buick Skylark Custom 1993 - IAC Valve Connections
Inspect carefully for loose or corroded connections.
Buick Skylark Custom 1993 - PCV Valve
An incorrect PCV valve may cause incorrect idle speed.
Buick Skylark Custom 1993 - CODE 41 - 1X REFERENCE CIRCUIT (2.3L)
Ignition module sends a signal to ECM once per revolution to indicate crankshaft position. ECM uses this information to determine when to pulse injectors for cylinders No. 2 and 3. This signal can be described as a synchronization signal and is called 1X reference because it occurs once per revolution.
Ignition module applies 5 volts from terminal "G" to ECM 7X reference terminal and, in effect, switches this circuit to ground for a short period of time, 125 degrees before TDC of cylinders No. 2 and 3. Code 41 is set if ECM receives (8) 2X reference pulses without a 1X reference pulse. When Code 41 is present, ECM pulses injectors in simultaneous mode.
NOTE: Test numbers refer to numbers on diagnostic chart.
- This determines if ECM recognizes a fault. If a Code 41 is not set here, problem is intermittent and could be caused by a loose connection.
- This step simulates 1X signal. If circuit and ECM are okay, ECM should recognize voltage drop as test light probe is removed. This step will only give accurate results if:
- Chart sequence is used (ignition off or ignition on).
- Scan tester is set to 1X reference.
- Terminal "G" is contacted using test light probe.
ECM will only recognize up to 4 simulated 1X pulses under this test condition.
- If ECM did not recognize simulation of 1X signal, circuit may be open or shorted to ground or voltage. If circuit is okay, ECM is faulty.
- Step 2 indicated 1X circuit is okay and ECM is capable of recognizing simulated 1X reference pulse. This indicates either a poor connection at ignition module terminal "G" or a faulty ignition module caused Code 41 to occur.
Buick Skylark Custom 1993 - Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Inspect ECM harness 1X connector terminal and ignition module terminal "G" for improperly formed or damaged terminals, poor terminal to wire connection and damaged harness. Code 41 will set if improper ignition module is installed.
Buick Skylark Custom 1993 - CODE 42 - EST CIRCUIT OPEN OR GROUNDED (2.3L)
Code 42 indicates ECM has seen an open or short to ground in HEI EST or by-pass circuit.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks if ECM recognizes a fault. If a Code 42 is not set here, an intermittent problem exists and could be caused by a loose connection.
- With ECM disconnected, ohmmeter should indicate less than 500 ohms, which is normal resistance for ignition module. A higher resistance indicates a fault in circuit No. 423, poor ignition module connection or faulty ignition module.
- If test light was illuminated when connected from 12 volts to ECM harness by-pass terminal, either circuit No. 423 is shorted to ground or ignition module is faulty.
- Checks if ignition module switches when by-pass circuit is energized by 12 volts through test light. If ignition module switches, ohmmeter reading should switch from less than 500 ohms to greater than 8000 ohms.
- Disconnecting ignition module should cause ohmmeter to indicate as if it were monitoring an open circuit (infinite reading). If ohmmeter indicates anything other than infinity, circuit No. 423 is shorted to ground.
Buick Skylark Custom 1993 - Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation or wire broken inside insulation. Inspect ECM harness connectors for backed-out by-pass or EST terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
Buick Skylark Custom 1993 - CODE 43, KNOCK SENSOR ERROR
NOTE: Knock sensor testing has been updated per TSB 93-6-21, dated December 16, 1992.
NOTE: Test numbers refer to numbers on diagnostic chart.
- If conditions for code exist, SERVICE ENGINE SOON light will be on.
- If engine has an internal problem, sensor may be responding to mechanical noise.
- Checks knock sensor activity. Scan displays knock sensor activity in counts (about 35-50 at idle). Counts should rise as engine speed increases.
- Checks internal resistance of knock sensor.
- Checks knock sensor connections. A faulty connection or component will set a Code 43.
Buick Skylark Custom 1993 - Diagnostic Aids
Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connections or damaged harness. Perform intermittent check by monitoring circuit and code status while wiggling related wiring and connectors. If failure is induced, monitored circuit status will change rapidly and/or related code will set.
Buick Skylark Custom 1993 - CODE 44 - LEAN EXHAUST INDICATION
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 Skylark Custom 1993 - 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 Skylark Custom 1993 - O2 Sensor Wire
O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.
Buick Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 CODE 44 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body O2 Signal A12 Black O2 Ground B6 Tan 2.3L "N" Body O2 Signal A12 Purple O2 Ground B6 Tan
Buick Skylark Custom 1993 - CODE 45 - RICH EXHAUST INDICATION
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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 - TPS
An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.
Buick Skylark Custom 1993 - 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 Skylark Custom 1993 - 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 Skylark Custom 1993 CODE 45 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION
Application ECM Terminal Wire Color 2.3L "L" Body O2 Signal A12 Black O2 Ground B6 Tan 2.3L "N" Body O2 Signal A12 Purple O2 Ground B6 Tan
Buick Skylark Custom 1993 - 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 Skylark Custom 1993 - CODE 52 - FAULTY CAL-PAK
Ensure all pins are fully inserted in socket. If pins are okay, replace CAL-PAK, clear memory and recheck. If Code 51 reappears, replace control module.
Buick Skylark Custom 1993 - CODE 53 - SYSTEM OVERVOLTAGE (2.3L)
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 ECM battery voltage terminal is not within specification, check and repair charging system.
Buick Skylark Custom 1993 CHARGING SYSTEM SPECIFICATIONS
Engine Minimum Charge Maximum Charge 2.3L 10.0 17.0
Buick Skylark Custom 1993 - CODE 55 - ECM ERROR
Ensure correct MEM-CAL or PROM is being used and that it is properly installed. If so, replace control module. Clear codes, confirm closed loop operation and check operation of SERVICE ENGINE SOON light.
Buick Skylark Custom 1993 - CODE 65 - INJECTOR CURRENT LOW (2.3L)(1 OF 2)
ECM has 2 injector driver circuits, each controlling a pair of injectors (1 and 4 or 2 and 3). ECM monitors current of each injector driver circuit by measuring voltage drop through a fixed resistor. ECM is able to control voltage drop. Current through each driver is allowed to rise to peak of 4 amps, enabling injectors to open quickly; current is then reduced to one amp, holding injectors open. This is called "peak and hold". If current cannot reach a 4-amp peak, Code 65 is set. This code is also set if an injector driver circuit is shorted to voltage.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Following conditions must be present to set Code 65:
- 4-amp injector current was not reached on each circuit.
- Battery voltage greater than 9 volts.
- Injectors pulsed on longer than calibrated pulse width.
- Above conditions met for 20 seconds.
- Checks ECM and harness wiring to 3-terminal injector harness connector.
- This tests for open injector harness or injector.
- Results of step 2) will determine which branch to follow on Code 65 flow chart (2 of 2).
- Each harness was confirmed as being okay in steps 2) and 3). This test will check remainder of circuit from injectors to ECM.
NOTE: Although shorted harness or injector (zero ohms) will not set a Code 65, problem should be corrected if discovered. - Identifies cause of high resistance found in step 3). A short or low resistance will not cause Code 65 but should be corrected.
- This tests for grounded "peak and hold" jumpers. This condition would allow injectors to pulse, but it would not allow "peak and hold" operation as current would not flow through resistor in ECM.
Buick Skylark Custom 1993 - Diagnostic Aids
An open in injector drive or "peak and hold" circuits or ECM drive circuits shorted to voltage will cause a Code 65 to be set and also cause misfire due to an inoperative pair of injectors. "Peak and hold" circuits shorted to ground will cause a Code 65 to set while allowing injectors to pulse. An intermittent problem would have to be present for at least 20 seconds to set Code 65.
Buick Skylark Custom 1993 - CODE 65 - INJECTOR CURRENT LOW (2.3L)(2 OF 2)
NOTE: Test numbers refer to numbers on diagnostic chart.
- 8) This checks for short to voltage in injector driver circuits.
- 9) Determines if injector driver circuits are shorted to ground.
- 10) This checks output at ECM to determine if injector driver circuits are okay.
- 11) Checks for proper continuity of "peak and hold" jumpers circuits.
Buick Skylark Custom 1993 - CODE 66 - A/C PRESSURE SENSOR (2.3L)
A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from ECM and returns an input signal to ECM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.9 volts. ECM will disable A/C if code 66 is present.
NOTE: Test numbers refer to numbers on diagnostic chart.
- Checks voltage signal from A/C pressure sensor to ECM.
- 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 ECM.
- Checks to see if low voltage signal was due to an open in sensor circuit or in 5-volt reference; previous step eliminated pressure sensor as a possible cause.
Buick Skylark Custom 1993 - 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 ECM.
Buick Skylark Custom 1993 - CODE 85 - PROM ERROR & CODE 87 - EEPROM ERROR
Ensure all ECM connectors are fully inserted in socket. If okay, have ECM reprogrammed using appropriate equipment. If equipment is not available, have ECM serviced through dealership.
Buick Skylark Custom 1993 - 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.