Honda Civic CRX HF 1991 - 1991 ENGINE PERFORMANCE Self-Diagnostics

Honda Civic CRX HF 1991 - INTRODUCTION

If no faults were found while performing BASIC TESTING , proceed with self-diagnostics. If no fault codes or only pass codes are present after entering self-diagnostics, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

Honda Civic CRX HF 1991 - SELF-DIAGNOSTIC SYSTEM Hard Failures

Hard failures cause CHECK ENGINE light to illuminate and remain on until problem 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 unit will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.

Honda Civic CRX HF 1991 - Intermittent Failures

Intermittent failures may cause CHECK ENGINE light to flicker or illuminate and go out after the intermittent fault goes away. However, the corresponding trouble code will be retained in ECU memory. If related fault does not reoccur within 50 starter operations, related trouble code will be erased from control unit memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Honda Civic CRX HF 1991 - CHECK ENGINE LIGHT

All models are equipped with a CHECK ENGINE light. As a bulb check, light illuminates when ignition is on and engine is not running. CHECK ENGINE light also illuminates when a system failure has been detected and a corresponding trouble code has been set in ECU memory. Not all trouble codes will activate CHECK ENGINE light. If CHECK ENGINE light is on and no codes are flashed by LED on ECU, back-up system is in operation. See TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Honda Civic CRX HF 1991 - RETRIEVING CODES

When the Check Engine warning light has been reported on, pull down the passenger's side carpet from under the dashboard, turn the ignition on, and observe the LED on the top of the ECU. The LED indicates a system failure code by blinking frequency. The ECU LED can indicate any number of simultaneous component problems by blinking separate codes, one after another. See Fig. 1 .

Proceed to appropriate code for testing. See TROUBLE CODE IDENTIFICATION CHART . All voltage tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless specifically stated differently in testing procedures.

Fig. 1: Honda Civic CRX HF 1991 - Component Locations - ECU LED Location & Blinking Frequency Examples

Honda Civic CRX HF 1991 - TROUBLE CODE DEFINITION

Honda Civic CRX HF 1991 TROUBLE CODE IDENTIFICATION CHART

Code (1)	System Affected	Probable Cause
0 (2)	ECU	No signal to ECU
1	O2 Sensor	Open or short signal circuit
3	MAP Sensor	Electrical problem in MAP sensor
4	Crank Angle Sensor	Problem in CRANK sensor circuit
5	MAP Sensor	Mechanical problem in MAP sensor
6	Coolant Temp. (TW) Sensor	Open or shorted signal circuit
7	Throttle Angle Sensor	Open or shorted signal circuit
8	TDC Position Sensor	Problem in TDC sensor circuit
9	No. 1 Cyl. Position (1.6L PFI)	Problem in CYL sensor circuit
10	Intake Air Temperature	Open or shorted signal circuit
12	EGR System (1.5L A/T - Calif.)	No EGR action
13	Atmospheric Pressure (PA)	Open or shorted signal circuit
14	Electronic Air Control Valve (EACV)	Problem in EACV circuit
15	Ignition Output Signal	Open or shorted signal circuit
16	Fuel Injector	Open or shorted signal circuit
17	Vehicle Speed Sensor (VSS)	No VSS signal
19	Lock-Up Control Solenoid Valve (A/T)	Open or shorted signal circuit
20	Electrical Load Detector	Open or shorted signal circuit
(1) If codes other than these are indicated, repeat self-diagnosis. If code(s) reappear, substitute a known good ECU, and recheck codes. If code(s) clear, replace ECU. (2) NO CHECK ENGINE LIGHT or CHECK ENGINE LIGHT ON, LED WON'T FLASH CODE .

Honda Civic CRX HF 1991 - CLEARING CODES

To reset ECU, remove hazard fuse located in main fuse block. Leave fuse out for 10 seconds to reset ECU.

Honda Civic CRX HF 1991 ECU RESET FUSE CHART

Model	Fuse	Location
Accord	BACK-UP	(1)
Civic	ECU	(2)
Prelude	CLOCK	(1)
(1) Underhood fuse/relay box. (2) Main fuse block.

Honda Civic CRX HF 1991 - ECU LOCATION

ECU is located under carpet in passenger-side footwell.

Honda Civic CRX HF 1991 - DIAGNOSTIC CODES NO CHECK ENGINE LIGHT

1. Turn ignition on. If oil pressure light is on, go to step 2). If light is off, inspect fuse No. 1. If fuse is okay, repair open circuit in Yellow wire between fuse and combination meter.
2. Turn ignition off. Connect ECU Test Harness (07999-PD6000A ) between ECU and connector. See Fig. 2 . Connect terminal B6 to ground. See Fig. 3 . Turn ignition on. If CHECK ENGINE light is now on, go to step 3). If light is off, replace light bulb or repair open in Green/Red wire between ECU terminal A13 and combination meter.
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   Fig. 2: Honda Civic CRX HF 1991 - Component Locations - Connecting PGM-FI Test Harness (07999-PD6000A)
   
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   Fig. 3: Honda Civic CRX HF 1991 - Component Locations - Identifying ECU Terminals
   

3. Individually measure voltage between ground and ECU terminals A2, A4, A16 and A18. If less than one volt is present, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU. If more than one volt is present, repair open in wire between ECU and thermostat housing ground having more than one volt.

Honda Civic CRX HF 1991 - CHECK ENGINE LIGHT ON, LED WON'T FLASH CODE

1. Turn ignition off. Remove and inspect ECU fuse, HAZARD fuse (main fuse block) and fuse No. 14 (underdash fuse block). Inspect ground connections at thermostat housing or Brown/Black and Black/Red wires at connector located on right front strut tower.
2. Turn ignition on. Verify CHECK ENGINE light stays on for 2 seconds. If light does not stay on for 2 seconds, check for poor connections and loose wires at main relay, ECU fuse or fuse No. 14. If CHECK ENGINE light comes on, check ECU LED inspection light for codes. If codes are present, repair trouble code(s). If no code(s) are present or if LED does not flash, go to next step.
3. Start engine. If engine does not start, go to step 4). If engine starts, turn ignition off. Disconnect ECU connector "B". Turn ignition on. Verify if CHECK ENGINE light is on. If light is on, repair short to ground in Green/Orange wire between ECU terminal B6 and combination meter. If light does not turn on, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.
4. If engine does not start, turn ignition on. Individually disconnect 3-wire connectors at MAP, throttle angle and EGR valve lift (1.5L A/T California) sensors. If CHECK ENGINE light turns off while disconnecting connector from any sensor, replace particular sensor. If light stays on throughout, go to step 5).
5. Reconnect all sensor connectors. Disconnect 3-wire connector to Atmospheric Pressure (PA) sensor. Check if LED is flashing Code 13. If Code 13 is present, replace PA sensor. If Code 13 is not present, go to step 6).
6. Turn ignition off. Connect ECU Test Harness (07999-PD6000A ) to ECU main harness side only. See Fig. 2 . Check continuity between ground and terminals C13 and C15. See Fig. 3 . If continuity is present, repair short in Yellow/Red wire between ECU and MAP sensor or in Yellow/White wire between ECU and PA, throttle angle or EGR valve lift sensor. If continuity is not present, go to step 7).
7. Reconnect 3-wire PA sensor connector. Connect ECU Test Harness (07999-PD6000A ) connectors "A", "B" and "C" to ECU. See Fig. 2 . Turn ignition on. Measure voltage between ground and ECU terminals A16 and A18. See Fig. 3 . If less than one volt is present, go to step 8). If more than 1 volt is present, repair open in wire between ECU terminals A16 and A18 and thermostat housing (ground).
8. Measure voltage between ECU terminals A13, A15 and A18. If battery voltage is present, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU. If battery voltage is not present, repair open in Yellow/Black wire between ECU terminals A13 and A15 and main relay. Check main relay and connectors.

Honda Civic CRX HF 1991 - CODE 1 - O2 SENSOR

1. Turn ignition off. Reset ECU by removing ECU fuse in main fuse/relay block for 10 seconds. Check fuel pressure regulator. See SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE Section. Repair or replace as necessary. Warm engine to normal operating temperature (cooling fan comes on).
2. On 1.5L, block rear wheels, and set parking brake. Jack up front of vehicle, and support with safety stands. Place transmission in 2nd gear, and run engine at 2400 RPM for 15 minutes without closing throttle completely.
3. On 1.6L, bring engine to operating temperature (cooling fan comes on). Hold engine RPM at 1500 RPM (minimum) for 15 minutes without closing throttle completely.
4. On all models, check if CHECK ENGINE light is on and if LED indicates Code 1. If light is not on and Code 1 is not present, problem is intermittent. Test drive, and check light again. If light is on and Code 1 is present, inspect for poor connection and loose ground at thermostat housing. Repair as necessary. If connections and wires are okay, go to next step.
5. Disconnect O2 sensor connector. Connect voltmeter to vehicle ground and O2 sensor connector. With engine at normal operating temperature and while watching voltmeter, hold engine speed at 4000 RPM for 10 seconds and then release throttle completely.
6. Voltage should be greater than .6 volt at wide open throttle and less than .4 volt at closed throttle. If voltage is not as specified, replace O2 sensor. If voltage is within specifications, proceed to next step.
7. Turn ignition off. Reconnect O2 sensor connector. Attach ECU Test Harness (07999-PD6000A ) between ECU and ECU connector. See Fig. 2 . Connect voltmeter between ECU terminals A18 (-) and C16 (+). See Fig. 3 . Restart and warm engine to normal operating temperature. Hold engine speed at 4000 RPM for 10 seconds, and then close throttle completely.
8. Voltage should be greater than .6 volt at wide open throttle or 4000 RPM and less than .4 volt at closed throttle. If voltage is not as specified, repair short or open in White wire between ECU and O2 sensor. If voltage is within specifications, substitute a known good ECU. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 3 - MAP SENSOR

1. Turn off ignition. Remove ECU fuse for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 3. If LED is flashing Code 3, go to next step. If LED is not flashing Code 3, problem is intermittent. Check connectors at MAP sensor and ECU.
2. Turn ignition off. Disconnect 3-wire MAP sensor connector. Turn ignition on. Measure voltage between Yellow/Red (+) wire and ground. If reading is about 5 volts, go to step 4).
3. If reading is not approximately 5 volts, check for open in Yellow/Red (+) wire between ECU terminal C15 and MAP sensor. If wire is okay, substitute a known good ECU, and recheck. If specified voltage is now available, replace original ECU.
4. Measure voltage between Yellow/Red (+) and Green/White (-) wires. If voltage is about 5 volts, go to step 5). If reading is not about 5 volts, check for open in Green/White wire between ECU terminal C14 and MAP sensor. If wire is okay, substitute a known good ECU, and recheck. If specified voltage is now present, replace original ECU.
5. Measure voltage between White (+) and Green/White (-) wires. If reading is not about 5 volts, go to step 7). If measured voltage is about 5 volts, turn ignition off. Reconnect 3-wire MAP sensor connector. Connect ECU Test Harness (07999-PD6000A ) between ECU and ECU connector. See Fig. 2 . Turn ignition on. Measure voltage between terminal C11 (+) and C14 (-). See Fig. 3 . If reading is not about 3 volts, replace MAP sensor.
6. If about 3 volts are present between terminals C11 and C14, substitute a known good ECU, and recheck. If specified voltage is now available, replace original ECU.
7. If voltage measured in step 5) is not about 5 volts, repair open or short in White wire between ECU terminal C11 and MAP sensor. If wire is okay, substitute a known good ECU, and recheck. If specified voltage is now available, replace original ECU.

Honda Civic CRX HF 1991 - CODE 4 - CRANK ANGLE SENSOR Civic 1.5L

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 4. If LED is flashing Code 4, go to next step. If LED is not flashing Code 4, problem is intermittent. Check connectors at distributor and related circuits.
2. Turn ignition off. Disconnect 6-wire TDC/CRANK sensor connector at distributor. Measure resistance between terminals "D" and "E". See Fig. 4 . If resistance is not 350-550 ohms, replace distributor assembly. If resistance is within specification, check for continuity between ground and terminals "D" and "E". If continuity exists, sensor is shorted to ground. Replace distributor assembly.
3. If continuity to ground does not exist in step 2), reconnect 6-wire connector. Connect ECU Test Harness (07999-PD6000A ) to main wire harness connector side only. See Fig. 2 . Measure resistance between terminals C1 and C2. See Fig. 3 . If resistance is not 350-550 ohms, repair Orange and/or White wires.
4. If resistance is within specification, check for continuity between terminal C1 and ground. If continuity exists, repair short in Orange wire between ECU terminal C1 and distributor connector. If continuity does not exist, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.
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   Fig. 4: Honda Civic CRX HF 1991 - Component Locations - TDC/CRANK Sensor Connector Terminal ID (Civic 1.5L)
   

Honda Civic CRX HF 1991 - Civic 1.6L

1. Turn off ignition. Remove ECU fuse for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 4. If LED is flashing Code 4, go to next step. If LED is not flashing Code 4, problem is intermittent. Check connectors at distributor and related circuits.
2. Turn ignition off. Unplug 8-wire TDC/CRANK/CYL sensor connector at distributor. Measure resistance between terminals "C" and "D". See Fig. 5 . If resistance is not 350-550 ohms, replace distributor assembly. If resistance is within specification, check for continuity between ground and terminals "C" and "D". If continuity exists, sensor is shorted to ground. Replace distributor assembly.
3. If continuity to ground does not exist in step 2), reconnect 8-wire connector. Connect ECU Test Harness (07999-PD6000A ) to main harness side only. See Fig. 2 . Measure resistance between terminals B10 and B12. See Fig. 3 . If resistance is not 350-550 ohms, repair Orange and/or White wires.
4. If resistance is within specification, check for continuity between terminal B10 and ground. If continuity exists, repair short in Orange wire between ECU terminal B10 and distributor connector. If continuity does not exist, substitute a known good ECU. If condition is corrected, replace original ECU.
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   Fig. 5: Honda Civic CRX HF 1991 - Component Locations - TDC/CRANK/CYL Sensor Connector Terminal ID (Civic 1.6L)
   

Honda Civic CRX HF 1991 - CODE 5 - MAP SENSOR

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 5. If LED is flashing Code 5, go to next step. If LED is not flashing Code 5, problem is intermittent. Check vacuum hoses, pipes and connections. Ensure all connectors are secure.
2. Turn ignition off. Connect vacuum pump/gauge to MAP sensor hose at throttle body. Apply vacuum. If vacuum holds, go to step 3). If vacuum does not hold, attach vacuum pump/gauge directly to MAP sensor. Apply vacuum. If vacuum does not hold, replace MAP sensor. If vacuum holds, check MAP sensor vacuum hose for cracks, splits and looseness. Repair as necessary.
3. Check vacuum supply to MAP sensor with engine running. If vacuum is not present, repair hose or clear restriction from throttle body. If vacuum supply is okay, turn ignition off. Connect ECU Test Harness (07999-PD6000A ) between ECU and ECU connector. See Fig. 2 . Measure voltage between terminals C11 (+) and C14 (-). See Fig. 3 . If reading is about 3 volts, go to next step. If reading is not about 3 volts, replace MAP sensor.
4. Start engine, and allow to idle. Measure voltage between terminals C11 (+) and C14 (-). If reading is not about 1 volt, replace MAP sensor. If reading is about 1 volt, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 6 - COOLANT TEMPERATURE (TW) SENSOR

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 6. If LED is flashing Code 6, go to next step. If LED is not flashing Code 6, problem is intermittent. Check connectors at TW sensor and related circuits.
2. Warm engine to normal operating temperature (cooling fan comes on). Disconnect 2-wire connector from TW sensor. Turn ignition off. Measure resistance between terminals on TW sensor. If resistance is not between 200-400 ohms, replace sensor. If sensor resistance is okay, go to next step.
3. Turn ignition on. Measure voltage between ground and Red/White wire on sensor harness. If voltage is not about 5 volts, go to step 5). If voltage is about 5 volts, measure voltage between Red/White (+) and Green/White (-) wires. If reading is not about 5 volts, repair open in Green/White wire between ECU and coolant sensor.
4. If voltage reading from Green/White wire to Red/White wire of coolant sensor harness is about 5 volts, substitute a known good ECU. If Code 6 does not reset, replace original ECU.
5. If voltage reading from ground to Red/White wire of coolant sensor harness is not about 5 volts in step 3), repair short in Red/White wire between ECU terminal C6 and TW sensor.

Honda Civic CRX HF 1991 - CODE 7 - THROTTLE ANGLE SENSOR

1. Turn ignition off. Remove appropriate fuse for 10 seconds to reset ECU. See ECU RESET FUSE CHART . Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 7. If Code 7 is present, go to next step. If Code 7 is not present, problem is intermittent. Check connectors at throttle angle sensor and related circuits.
2. Turn ignition off. Disconnect 3-wire connector at throttle angle sensor. Turn ignition on. Measure voltage between Yellow/White (+) and Green/White (-) wires. If voltage is not about 5 volts, go to step 6). If voltage is about 5 volts, turn ignition off. Reconnect sensor connector. Connect ECU Test Harness between ECU and ECU connector. See Fig. 2 .
3. Turn ignition on. Apply 20 in. Hg to throttle dashpot diaphragm. Measure voltage between positive terminal C7 and negative terminal C12. See Fig. 3 . Voltage should be .5 volt at closed throttle and about 4.5 volts at wide open throttle. Transition between lower and upper voltage specification as throttle is depressed should be smooth.
4. If throttle sensor responds as indicated, substitute a known good ECU. If condition is corrected, replace original ECU. If sensor does not respond as indicated in step 3), replace throttle sensor or repair open or short in Red/Blue wire between ECU terminal C7 and throttle sensor.
5. If voltage reading between Yellow/White (+) and Green/White (-) wires in step 2) is not about 5 volts, measure voltage between ground and Yellow/White wire terminal. If voltage is now about 5 volts, repair open in Green/White wire between ECU terminal C12 and throttle sensor. If reading is not about 5 volts, turn ignition off.
6. Connect ECU Test Harness between ECU and ECU connector. Turn ignition on. Measure voltage between terminal C13 and terminal C12. If voltage is about 5 volts, repair open Yellow/White wire between ECU terminal C13 and throttle sensor. If reading is not about 5 volts, substitute a known good ECU. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 8 - TDC SENSOR

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 8. If LED is flashing Code 8, go to next step. If LED is not flashing Code 8, problem is intermittent. Check connectors at distributor and related circuits.
2. If light is on, turn ignition off. Disconnect sensor harness connector at distributor. Measure resistance between sensor terminals "B" and "C" ("A" and "B" on 1.6L). See Fig. 4 or Fig. 5 . If resistance is not 350-550 ohms, replace distributor assembly. If resistance value is within specification, individually check for continuity between ground and same terminals. If continuity exists, sensor is shorted to ground. Replace distributor assembly.
3. Reconnect sensor connector. Connect ECU Test Harness (07999-PD6000A ) to main wiring harness side only. Measure resistance between terminals C3 and C4. If resistance is not 350-550 ohms, repair open or short in Orange/Blue and/or White/Blue wire. If resistance is within specification, substitute a known good ECU, and retest. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 9 - CYL SENSOR Civic 1.6L

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 9. If LED is flashing Code 9, go to next step. If LED is not flashing Code 9, problem is intermittent. Check connectors at distributor and related circuits.
2. If light is on, turn ignition off. Disconnect 8-wire sensor connector nearest sensor. Measure resistance between terminals "F" and "G". See Fig. 5 . If reading is not 350-550 ohms, replace distributor assembly. If reading is within specification, proceed to next step.
3. Check continuity between ground and terminals "F" and "G". If continuity exists, replace distributor assembly. If no continuity exists, proceed to next step.
4. Reconnect sensor connector. Attach ECU Test Harness (07999-PD6000A ) to main wire harness side only. Check resistance between connector terminals C1 and C2. Resistance should be 350-550 ohms.
5. If resistance is not within specification, repair open in Blue/Green or Blue/Yellow wires between ECU terminal C1 and distributor connector. If resistance is within specification, go to next step.
6. Check continuity between ground and ECU terminal C1. If continuity exists, repair short in Blue/Green wire between ECU terminal C1 and distributor connector. If no continuity exists, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 10 - AIR TEMPERATURE (TA) SENSOR

1. Turn ignition off. Remove appropriate fuse for 10 seconds to reset ECU. See ECU RESET FUSE CHART . Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 10. If Code 10 is present, go to next step. If Code 10 is not present, problem is intermittent. Check connectors at TA sensor and related circuits.
2. Turn ignition off. Disconnect TA sensor connector, and measure resistance across TA sensor terminals. If resistance reading is not 1000-4000 ohms, replace TA sensor. If resistance reading is as specified, disconnect ohmmeter, and turn ignition on. Measure voltage between ground and Red/Yellow wire terminal. If voltage is about 5 volts, go to step 3). If voltage is not about 5 volts, go to step 4).
3. Measure voltage between Red/White (+) and Green/White (-) wires. If voltage is not about 5 volts, repair open circuit in Green/White wire between ECU terminal C12 and TA sensor. If voltage is about 5 volts, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.
4. Repair open or short in Red/Yellow wire between ECU terminal C5 and TA sensor. If wire is okay, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 12 - EGR SYSTEM Civic 1.5L A/T (California)

1. Verify if CHECK ENGINE light is on and if LED is flashing Code 12. Check harness and connections between EGR valve and ECU. Check vacuum hoses for cracks, splits and looseness. Repair as necessary. Remove ECU fuse for 10 seconds to reset ECU.
2. Warm engine to normal operating temperature (cooling fan on). Disconnect vacuum hose No. 16 from EGR valve. Using a hand-held vacuum pump, apply vacuum to EGR valve. If vacuum does not hold and engine does not stall, clean blocked EGR passages or replace faulty EGR valve.
3. If vacuum holds and engine stalls in step 2), disconnect Constant Vacuum Control (CVC) vacuum hose, and connect to vacuum gauge. Start engine. If about 8 in. Hg is not present, check vacuum hoses and connecting pipes. If vacuum is present, reconnect hose between vacuum chamber and EGR solenoid.
4. Verify vacuum supply to EGR valve. If vacuum is now present at EGR valve, check for short in Red wire between ECU terminal A10 and EGR control solenoid. If wire is okay, replace solenoid. If vacuum is not present, turn engine off. Disconnect 4-wire connector from control box. Supply battery voltage to terminal "D", and ground to terminal "C" at control box (solenoid side of harness). See Fig. 6 . Start engine and check EGR valve for 8 in. Hg. If vacuum is present, go to step 6).
5. If vacuum is not present, remove control box cover. Disconnect vacuum hose between air chamber and solenoid valve. Connect vacuum gauge to air chamber. Start engine. If about 8 in. Hg is not present, check hose routing of EGR system. If vacuum is present, replace CVC valve.
6. Measure voltage between ground and Black/Yellow wire terminal of harness. If battery voltage is not present, repair open in Black/Yellow wire between solenoid valve and fuse No. 14. If battery voltage is present, turn ignition off. Connect Test Harness (07GMJ-ML80100) between EGR valve lift sensor and sensor connector. Disconnect vacuum hose from EGR valve.
7. Turn ignition on. Measure voltage between Red (+) and Green (-) terminals of harness. If about 5 volts are indicated, go to step 10). If about 5 volts are not indicated, measure voltage between ground and Red (+) harness terminal.
8. If 5 volts are indicated, repair open in Green/White wire between ECU terminal C12 and sensor. If about 5 volts are not indicated, repair open in Yellow/White wire between ECU terminal C13 and EGR valve lift sensor. If wire is okay, substitute a known good ECU. If condition is corrected, replace original ECU.
9. If voltage is about 5 volts, measure voltage between White (+) and Green (-) terminals of harness. If about one volt is not indicated, replace EGR valve or repair short in Yellow wire between ECU terminal C8 and EGR valve lift sensor. If about one volt is indicated, turn ignition off.
10. Connect ECU Test Harness between ECU and ECU connector. See Fig. 2 . Turn ignition on. Measure voltage between terminals C8 (+) and C12 (-). See Fig. 3 . If about one volt is not indicated, repair open Yellow wire between ECU terminal C8 and sensor.
11. If about one volt is indicated, start engine, and allow to idle. Connect terminals A10 (+) and A2 (-) using jumper. If engine does not stall, repair open in Red wire between ECU terminal A10 and EGR control solenoid valve. If engine stalls, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.

Fig. 6: Honda Civic CRX HF 1991 - Component Locations - EGR Solenoid Terminal ID (Civic 1.5L A/T - Calif.)

Honda Civic CRX HF 1991 - CODE 13 - ATMOSPHERIC PRESSURE (PA) SENSOR

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset. Turn ignition on. Verify if CHECK ENGINE light is on and if LED is flashing Code 13. If LED is flashing Code 13, go to next step. If LED is not flashing Code 13, problem is intermittent. Check connectors at PA sensor.
2. Turn ignition off. Disconnect harness from PA sensor. Measure voltage at harness between Yellow/White (+) terminal and ground. If reading is about 5 volts, go to next step. If reading is not about 5 volts, repair open in Yellow/White wire between ECU terminal C13 and PA sensor. If wire is okay, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.
3. Measure voltage between Yellow/White (+) and Green/White (-) terminals. If reading is about 5 volts, go to next step. If reading is not about 5 volts, repair open in Green/White wire between ECU terminal C12 and PA sensor. If wire is okay, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.
4. Measure voltage between Red/White (+) and Green/White (-) terminals. If reading is about 5 volts, go to next step. If reading is not about 5 volts, repair open in Red/White wire between ECU terminal C9 and PA sensor. If wire is okay, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.
5. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Turn ignition on. Verify if CHECK ENGINE light is on and if LED is flashing Code 13. If LED is flashing Code 13, replace PA sensor. If LED is still flashing Code 13, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 14 - ELECTRONIC AIR CONTROL VALVE (EACV)

1. Turn ignition off. Remove appropriate fuse for 10 seconds to reset ECU. See ECU RESET FUSE CHART . Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 14. If Code 14 is present, go to next step. If Code 14 is not present, problem is intermittent. Check connectors at EACV and related circuits.
2. Turn ignition off. Disconnect EACV connector. Check resistance between both connector terminals on EACV.
3. Resistance should be 8-15 ohms. If resistance is not within specification, replace EACV. If resistance is within specification, proceed to next step.
4. Check for continuity to ground on each EACV connector terminal. If continuity exists, replace EACV. If no continuity exists, turn ignition on. Measure voltage between positive Black/Yellow and negative Blue/Yellow terminals.
5. Check for battery voltage. If no battery voltage exists, proceed to step 6). If battery voltage exists, disconnect connector from ECU, and again check for battery voltage. If battery voltage still does not exist, substitute a known good ECU. If condition is corrected, replace original ECU. If battery voltage exists, repair short in Blue/Yellow wire between ECU terminal A11 and EACV.
6. If battery voltage is not present in step 5), measure voltage between ground and Black/Yellow wire terminal. If battery voltage is now present, proceed to step 7). If battery voltage still does not exist, repair open Black/Yellow wire between main relay and EACV.
7. If battery voltage exists, turn ignition off. Reconnect EACV connector. Connect ECU Test Harness connector "A" to main wire harness side only. Turn ignition on. Measure voltage between connector A11 (+) and A2 (-). If voltage does not exist, repair open in Blue/Yellow wire between ECU terminal A11 and EACV.
8. If battery voltage exists, connect and disconnect terminal A11 and A2. If EACV does not click when connector is connected and disconnected, replace EACV. If EACV clicks, substitute a known good ECU. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - CODE 15 - IGNITION OUTPUT SIGNAL

NOTE:

If engine will not start, continue cranking for 20 seconds to reproduce trouble code.

1. Turn ignition off. Remove appropriate fuse for 10 seconds to reset ECU. See ECU RESET FUSE CHART . Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 15. If Code 15 is present, go to next step. If Code 15 is not present, problem is intermittent. Check connector at distributor and related circuits.
2. Turn ignition off. Disconnect 2-wire connector at distributor. Turn ignition on. Measure voltage between ground and Black/Yellow wire terminal on wire harness side. If battery voltage is not present, repair open Black/Yellow wire between connector and ignition switch.
3. If battery voltage is present, turn ignition off. Reconnect 2-wire or 6-wire connector. Connect ECU Test Harness between ECU and ECU connector. See Fig. 2 . Turn ignition on. Individually measure voltage between negative terminal A18 and positive terminals B15 and B17. See Fig. 3 .

   NOTE:

   If wire between ignitor and ECU is shorted, ignitor may be damaged.

4. If approximately 10 volts is present, substitute a known good ECU, and retest. If condition is corrected, replace original ECU. If specified voltage is not present, check for short or open in White wire between distributor and ECU terminals B15 and B17. If wires are okay, replace ignitor unit.

Honda Civic CRX HF 1991 - CODE 16 - FUEL INJECTOR CIRCUIT Civic 1.5L

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Attempt to start engine. If engine does not start, go to step 3). Verify if CHECK ENGINE light is on and if LED is flashing Code 16. If LED is flashing Code 16, go to next step. If LED is not flashing Code 16, problem is intermittent. Check connectors at injectors, injector resistor and related circuits.

   NOTE:

   If engine will not start, continue cranking for at least 15 seconds to reset trouble code.

2. If engine will not start, verify if CHECK ENGINE LIGHT is on and LED indicates Code 16. If LED indicates Code 16, go to step 9). If LED does not indicate Code 16, refer to TESTS W/O CODES article. If engine starts, run and hold engine speed at 2000 RPM for 1 minute. Verify if CHECK ENGINE light is on and LED indicates Code 16.
3. Turn ignition off. Disconnect injector terminal connector. Measure resistance between injector terminals. Resistance should be .6-1.6 ohms. If resistance is not as specified, replace injector. If resistance is as specified, go to next step.
4. Connect voltmeter positive lead between injector Yellow/Black wire and ground. Turn ignition on. If battery voltage is present for 2 seconds, go to step 5). If battery voltage is not present, repair open in Yellow/black wire between main injector and main relay.
5. Turn ignition off. Disconnect 2-wire auxiliary injector connector. Measure resistance between auxiliary injector terminals. If resistance is not 6-10 ohms, replace injector. If resistance is within specification, turn ignition on. Connect voltmeter between auxiliary injector Yellow/Black wire (+) and ground.
6. If battery voltage is present within 2 seconds, go to step 7). If battery voltage is not present, repair open in Yellow/Black wire between 2-wire injector connector and main relay.
7. Connect voltmeter between Yellow (+) wire of auxiliary injector and ground. If reading is about 10 volts, go to step 8). If specified voltage is not available, repair open in Yellow wire between auxiliary injector and ECU terminals A1 and A3. If wire is okay, substitute a known good ECU, and recheck. If prescribed voltage is now present, replace original ECU.
8. Measure voltage between main injector Red wire and ground. If reading is about 10 volts, substitute a known good ECU, and recheck. If symptoms goes away, replace original ECU. If specified voltage is not available, repair open in Red wire between main injector and ECU terminals A5 and A7. If wire is okay, substitute a known good ECU, and recheck. If prescribed voltage is now available, replace original ECU.
9. Turn ignition off. Disconnect auxiliary injector connector. Measure resistance between auxiliary injector terminals. Resistance should be 6-10 ohms. If resistance is not as specified, replace auxiliary injector. If resistance is as specified, go to next step.
10. Turn ignition on. Measure voltage between auxiliary injector Yellow wire connector and ground. Reading should be about 10 volts. If voltage reading is as specified, go to step 11). If voltage is not as specified, repair open or short in Yellow wire between auxiliary injector and ECU terminals A1 and A3. If wire is okay, substitute a known good ECU, and recheck. If prescribed voltage is now present, replace original ECU.
11. Disconnect main injector terminal connector. Measure voltage between main injector Red wire terminal and ground. Reading should be about 10 volts. If reading is as specified, go to step 12). If reading is not as specified, repair short in Red wire between main injector and ECU terminals A5 and A7. If wire is okay, substitute a known good ECU, and recheck. If prescribed voltage is now present, replace original ECU.
12. Turn ignition off. Connect voltmeter between auxiliary injector Yellow/Black (+) wire and ground. Turn ignition on. If battery voltage is not present, go to step 13). If battery voltage is present for 2 seconds, substitute a known good ECU, and recheck. If prescribed voltage is now available, replace original ECU.
13. Turn ignition off. Connect ECU Test Harness between ECU and ECU connector. Individually connect ECU terminals A12, A14 and A18. Turn ignition on. If battery voltage is present at Yellow/Black wire of auxiliary injector, go to step 14). If battery voltage is not present at Yellow/Black wire of auxiliary injector, go to step 15).
14. Repair open in Black wire between ground terminals at thermostat housing and ECU terminals A2 and A4. If wires or connections are okay, substitute a known good ECU, and recheck. If prescribed voltage is now available, replace original ECU.
15. Repair open in Yellow/Black wire between auxiliary injector and main relay or repair open in Green/Black wire between main relay and ECU terminals A12 and A14. If wires are okay, replace main relay.

Honda Civic CRX HF 1991 - Civic 1.6L

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Start engine. If engine starts, go to next step. If engine does not start, go to step 4).
2. Verify if CHECK ENGINE light is on and LED indicates Code 16. If CHECK ENGINE light is not on and Code 16 is not present, problem is intermittent. Test drive may be necessary. Check for loose or poor connections at injectors, injector resistor and ground at left shock tower.
3. If CHECK ENGINE light is on and Code 16 is present, use stethoscope to check for clicking sound at each injector while engine is idling. If all injectors click, substitute a known good ECU. If condition is corrected, replace original ECU. If not all injectors are clicking, go to next step.
4. Turn ignition off. Disconnect injector terminal connectors. Check resistance of injectors. If resistance value is not 1.5-2.5 ohms, replace injector(s). If resistance values are within specification, turn ignition on. Measure voltage between ground and Red/Black wire at injector.
5. If battery voltage is not present, go to step 8). If battery voltage is present, measure voltage between following terminals.
   • Injector No. 1 - Red/Black (+) and Brown (-)
   • Injector No. 2 - Red/Black (+) and Red (-)
   • Injector No. 3 - Red/Black (+) and Light Blue (-)
   • Injector No. 4 - Red/Black (+) and Yellow (-)

   If battery voltage is not present, go to step 6). If battery voltage is present, disconnect 17-wire connector from ECU. If battery voltage is still present, repair short in wire between ECU terminals A1 (injector No. 1), A3 (injector No. 2), A5 (injector No. 3) or A7 (injector No. 4) and fuel injectors. If battery voltage is not present, substitute a known good ECU. If condition is corrected, replace original ECU.

6. Reconnect injector connector(s). Turn ignition off. Connect ECU Test Harness between ECU and ECU connector. See Fig. 2 . Turn ignition on. Measure voltage between negative terminal A2 and following positive terminals. See Fig. 3 .
   • Injector No. 1 - A1
   • Injector No. 2 - A3
   • Injector No. 3 - A5
   • Injector No. 4 - A7
7. If battery voltage is present, substitute a known good ECU. If condition is corrected, replace original ECU. If battery voltage is not present, repair open in wire between ECU terminals A1, A3, A5 or A7 and injector.
8. Turn ignition off. Disconnect injector resistor 6-wire connector. Turn ignition on. Measure voltage between ground and Yellow/Black wire terminal. If battery voltage is present, repair open in Red/Black wire between 2-wire connector and injector resistor. If wire is good, replace injector resistor. If battery voltage is not present, repair open in Yellow/Black wire between injector resistor and main relay.

Honda Civic CRX HF 1991 - CODE 17 - VEHICLE SPEED SENSOR (VSS)

1. Turn ignition off. Remove appropriate fuse for 10 seconds to reset ECU. See ECU RESET FUSE CHART . Road test vehicle. With transmission in 2nd gear, accelerate to 3500 RPM and then decelerate to 1500 RPM with throttle fully closed. Verify if CHECK ENGINE light is on and if LED is flashing Code 17. If Code 17 is present, go to next step. If Code 17 is not present, problem is intermittent. Check connectors and related circuits.
2. Block rear wheels, and set parking brake. Raise and support front of vehicle. Connect ECU Test Harness between ECU and ECU connector. See Fig. 2 . Turn ignition on.
3. Slowly rotate left front wheel and measure voltage between positive terminal B16 and negative terminal A18. See Fig. 3 . If voltmeter does not pulse, go to step 4). If voltmeter pulses from 0-5 volts, substitute a known good ECU, and recheck. If symptom/indication goes away, replace original ECU.
4. Repair open or short in Yellow/Red wire between ECU and VSS. If wire is okay, replace VSS. If voltage is still not as specified, substitute a known good ECU, and recheck. If specified voltage is now present, replace original ECU.

Honda Civic CRX HF 1991 - CODE 19 - LOCK-UP CONTROL SOLENOID Civic A/T

1. Turn ignition off. Remove ECU fuse for 10 seconds to reset ECU. Drive vehicle and observe CHECK ENGINE light. Verify if CHECK ENGINE light is on and if LED is flashing Code 19. If LED is flashing Code 19, go to next step. If LED is not flashing Code 19, problem is intermittent. Check connectors at lock-up solenoid and related circuits.
2. Turn ignition off. Connect ECU Test Harness between ECU and ECU connector. See Fig. 2 . Disconnect connector "A" from ECU side only. Disconnect 2-wire connector from lock-up control solenoid valve.
3. Check continuity between ECU terminal A8 and ground. See Fig. 3 . If continuity is present, repair short in Yellow wire between ECU terminal A8 and lock-up control solenoid valve 2-wire connector.
4. If continuity does not exist, reconnect solenoid connector. Measure resistance between terminals A8 and A18. If resistance is 14-25 ohms, substitute a known good ECU. If condition is corrected, replace original ECU.
5. If resistance is not as specified, check for continuity in Yellow wire between ECU terminal A8 and solenoid 2-wire connector. If continuity does not exist, repair open in Yellow wire. If continuity exists, replace faulty lock-up solenoid valve.

Honda Civic CRX HF 1991 - CODE 20 - ELECTRICAL LOAD DETECTOR

1. Turn ignition off. Remove appropriate fuse for 10 seconds to reset ECU. See ECU RESET FUSE CHART . Start engine, and turn on headlights with engine at idle. Verify if CHECK ENGINE light is on and if LED is flashing Code 20. If Code 20 is present, go to next step. If Code 20 is not present, problem is intermittent. Check for poor connections and loose wires.
2. Turn ignition off. Open lid of main fuse panel in engine compartment. Disconnect 3-wire electrical load detector. Turn ignition on. Measure voltage between Black/Yellow (+) and Black (-) wire terminals of harness. If battery voltage is present, go to step 4).
3. If battery voltage is not present, measure voltage between Black/Yellow wire and ground. If battery voltage is now present, repair open in Black wire between connector and ground. If battery voltage is not present, repair open Black/Yellow wire between fuse No. 14 and connector.
4. Turn ignition off. Connect ECU Test Harness between ECU and ECU connector. See Fig. 2 . Disconnect connector "B" from ECU side only. Connect Green/Red terminal of load detector harness connector to ground. Check for continuity between ECU terminal B19 and ground. See Fig. 3 . If continuity does not exist, repair open Green/Red wire between ECU connector terminal B19 and load detector connector.
5. If continuity exists, disconnect Green/Red terminal of 3-wire connector on Civic models. On all models, reconnect connector "B" to ECU. Turn ignition on. Measure voltage between Green/Red (+) and Black (-) terminals of load detector harness. If 4.5-5 volts is present, go to step 7). If 4.5-5 volts is not present, disconnect connector "B" from main wiring harness, not ECU. Measure voltage between positive terminal B19 and negative terminal A18.
6. If voltage is now 4.5-5 volts, repair short in Green/Red wire between ECU terminal B19 and load detector connector. If voltage is not 4.5-5 volts, substitute a known good ECU. If correct voltage is now available, replace original ECU.
7. Reconnect load detector connector. Start engine. Measure voltage between positive terminal B19 and negative terminal A18 under following conditions:
   • Headlight switch in 1st pos. - should be 2.5-3.5 volts.
   • Headlight switch in 2nd pos. - should be 1.5-2.5 volts.
8. If voltage is not as specified, replace faulty electrical load detector. If voltage is as specified, substitute a known good ECU, and retest. If condition is corrected, replace original ECU.

Honda Civic CRX HF 1991 - SUMMARY

If no hard fault codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to the TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnosis procedures.