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Engine Controls - Tests W/codes - 2.1l Pgm-Fi Honda Prelude III рестайлинг

Testing & Diagnostics 5 illustrations ~6171 words

INTRODUCTION

If no faults were found while performing the test procedures in the BASIC TESTING - FUEL INJECTED article, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE

CHECK ENGINE LIGHT

All models are equipped with a CHECK ENGINE light. As a bulb check, light will illuminate when the ignition is on and engine is not running. CHECK ENGINE light will also illuminate when a system failure has been detected, and a corresponding trouble code has been set in ECU memory. See RETRIEVING CODES .

Not all trouble codes will activate CHECK ENGINE light. If CHECK ENGINE light is on and no codes are flashed by LED on ECU, this indicates that back-up system is in operation. See TESTS W/O CODES article.

With ignition off, insert jumper wire between terminals of 2-pin service check connector. (Scheme 72) Turn ignition on and count flashes on CHECK ENGINE light.

See PRELUDE FUEL INJECTION TROUBLE CODE IDENTIFICATION CHART and proceed to appropriate code for testing. 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.

Scheme 72

Scheme 72: Check Engine Light
Scheme 72: Check Engine Light

ECU Indicator LED

If CHECK ENGINE light illuminates when engine is running, a system failure has been detected, and a corresponding trouble code has been set in ECU memory. Access ECU, located under carpet near passenger's side kick panel. Stored codes will be flashed by LED on ECU. To verify codes, see CHECK ENGINE LIGHT .

Not all trouble codes will activate CHECK ENGINE light. If CHECK ENGINE light is on and no codes are flashed by LED on ECU, this indicates that back-up system is in operation. See TESTS W/O CODES article.

ECU LOCATION

The ECU is located under carpet in passenger's side footwell.

TROUBLE CODE IDENTIFICATION MENU

Code (1)System AffectedProbable Cause
0 (2)ECUNo signal to ECU
1Heated Oxygen SensorProblem in O2 sensor circuit
3MAP SensorElectrical problem in MAP sensor
4Crank Angle SensorProblem in CRANK circuit of sensor
5MAP SensorMechanical problem in MAP sensor
6Coolant Temperature SensorOpen or shorted circuit signal
7Throttle Angle SensorOpen or shorted signal circuit
8TDC SensorProblem in TDC circuit of sensor
9No. 1 Cyl. Position SensorProblem in CYL ckt of sensor
10Intake Air TemperatureOpen or shorted circuit signal
12EGR SystemNo EGR action
13Atmospheric PressureOpen or shorted circuit signal
14Electronic Air Control (EACV)Open or shorted EACV ckt
15Ignition Output SignalOpen or shorted signal circuit
16Fuel InjectorOpen or shorted signal circuit
17Vehicle Speed SensorOpen or shorted signal circuit
41Oxygen Sensor HeaterProblem in O2 sensor circuit
43Fuel Supply SystemO2 sensor ckt problem or fuel system
(1) If codes other than the above are indicated, repeat self-diagnosis. If code(s) reappear, substitute with a known good ECU and recheck code(s). If code(s) clear, replace ECU. (2) NO CHECK ENGINE LIGHT, CHECK ENGINE LIGHT ON, LED DOES NOT FLASH CODES.
(1)If codes other than the above are indicated, repeat self-diagnosis. If code(s) reappear, substitute with a known good ECU and recheck code(s). If code(s) clear, replace ECU.
(2)NO CHECK ENGINE LIGHT, CHECK ENGINE LIGHT ON, LED DOES NOT FLASH CODES.

PRELUDE FUEL INJECTION TROUBLE CODE IDENTIFICATION CHART

Hard Failures

Hard failures cause CHECK ENGINE light to illuminate and remain on until the 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 unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely be encountered.

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.

CLEARING CODES

To reset ECU, remove CLOCK fuse (Prelude PGM-EFI). Leave fuse out for 10 seconds to reset ECU.

Scheme 73

Scheme 73: HARNESS CONNECTOR ID
Scheme 73: HARNESS CONNECTOR ID

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 13. If fuse is okay, repair open circuit in Yellow wire between fuse and combination meter.
  2. Turn ignition off. Connect ECU Test Harness between ECU and connector. (Scheme 73) Connect terminal A13 to ground. 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.
  3. Measure voltage individually between ground and ECU terminals A23, A24, A26, and B2. 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 the ECU and thermostat housing ground that had more than one volt.
  4. If CHECK ENGINE light illuminated in step 4), substitute a known good ECU. If condition is corrected, replace original ECU.

CHECK ENGINE LIGHT ON

  1. Turn ignition on. If CHECK ENGINE light stays on after 2 seconds, go to step 2). If light turns off after 2 seconds, problem is intermittent. Check for loose wires or poor connections at thermostat housing, main relay connector, ECU fuse (under-hood relay box) and No. 2 fuse (under-dash fuse box).
  2. Check for trouble code(s) at ECU LED inspection light. Repair trouble code(s) if present. If no trouble code(s) present, try to start engine. If engine starts, go to step 3). If engine does not start, go to step 4).
  3. If engine starts, turn ignition off. Disconnect connector "A" from ECU. Turn ignition on. If CHECK ENGINE light is on, repair short to ground in Green/Red wire between ECU and warning light. If light did not come on, substitute a known good ECU and retest. If condition is corrected, replace original ECU.
  4. If engine does not start, remove and inspect 10 amp ECU fuse in under-hood relay box and fuse No. 2 (15 amp) fuse in under-dash fuse box. Replace fuses if bad.
  5. Turn ignition on. Disconnect 3-wire connectors (one at a time) at MAP sensor, throttle angle sensor, and EGR valve lift sensor. If CHECK ENGINE light turns off while disconnecting connector from any of the sensors, replace that particular sensor. If light stayed on all the time, go to step 6).
  6. Turn ignition off. Connect ECU Test Harness between ECU and connector. (Scheme 73) Disconnect "D" connector from ECU side. Check continuity between terminal D19 and D20 to ground. If continuity is present, go to next step. If continuity is not present, go to step 8).
  7. Repair short in Red/White wire and/or Yellow/White wire between ECU terminals D19, D20 and MAP sensor, throttle angle sensor or EGR valve lift sensor.
  8. Reconnect ECU Test Harness connector "D" to ECU side. Turn ignition on. Individually ground terminals B2 and A26. If CHECK ENGINE light is still on, go to step 9). If light is not on, repair open in Black/Red and Brown/Black wires between ECU terminals A26, B2 and ground.
  9. Measure voltage between ECU terminals A25, B1 (positive) and A26 (negative). If battery voltage is present, substitute a known good ECU and recheck. If condition is corrected, replace original ECU. If battery voltage was not present, repair open in Yellow/Black wire between ECU terminals A25, B1 and main relay. Check main relay wiring and connectors.

Prelude 2.1L

  1. Turn ignition off. Reset ECU by removing BACK-UP fuse in under-hood relay box for 10 seconds. Start engine and warm to normal operating temperature (cooling fan comes on).
  2. Road test vehicle. With transmission in 2nd gear, accelerate for at least 5 seconds at wide open throttle. Then decelerate for at least 5 seconds with throttle completely closed. Verify if CHECK ENGINE light is on and if LED is flashing Code 1. If LED is flashing Code 1, perform test in «CODE 43, FUEL SUPPLY SYSTEM»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-tests-wcodes-21l-pgm-fi) . If LED is not flashing Code 1, problem is intermittent. Check connectors at O2 sensor, battery, and at ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box for 10 seconds to reset ECU. Start engine and warm to normal operating temperature (cooling fan on). 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 at ECU.
  2. Turn ignition off. Disconnect 3-wire connector from MAP sensor. Turn ignition on. Measure voltage between Red/White (positive) and negative Green (negative) terminals. If reading is about 5 volts, go to step 3). If reading is not about 5 volts, repair open in Red/White wire between ECU terminal D19 and MAP sensor. If wire is okay, substitute a known good ECU. If condition is corrected, replace original ECU.
  3. Measure voltage between Red/White (positive) and Blue/White (negative) terminals. If about 5 volts are present, go to step 4). If about 5 volts is not present, repair open in Blue/White wire between ECU terminal D21 and MAP sensor. If wire is okay, substitute a known good ECU. If condition is corrected, replace original ECU.
  4. Measure voltage between White/Blue (positive) and Blue/White (negative) terminals. If voltage is about 5 volts, go to step 5). If about 5 volts are not present, repair open in White/Blue wire between ECU terminal D17 and MAP sensor. If wire is okay, substitute a known good ECU. If condition is corrected, replace original ECU.
  5. Turn ignition off. Reconnect 3-wire connector to MAP sensor. Connect ECU Test Harness between ECU and ECU harness. (Scheme 73) Turn ignition on. Measure voltage between terminal positive D17 and negative D21. If reading is not about 3 volts, replace MAP sensor.
  6. If there is about 3 volts present, substitute a known good ECU and recheck. If condition is corrected, replace original ECU.

Scheme 74

Scheme 74: Prelude 2.1L
Scheme 74: Prelude 2.1L
  1. Turn ignition off. Remove or CLOCK fuse in the under-hood relay box 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 4-wire TDC/CRANK sensor connector nearest the sensor. Measure resistance across terminals "C" and "D" at sensor. (Scheme 74) If reading is not 700-1000 ohms, replace pulse generator assembly. If reading is within specification, proceed to next step.
  3. Check continuity between ground and sensor terminals "C" and "D" individually. If continuity exists on either terminal, sensor is shorted to ground. Replace pulse generator assembly. If no continuity exists, go to next step.
  4. Reconnect sensor connector. Connect ECU Test Harness to main harness side only. (Scheme 73) Check resistance between connector terminals B10 and B12. Resistance should be 700-1000 ohms.
  5. If resistance is not within specification, repair open in Blue/Yellow and/or Blue/Green wire. If resistance is within specification, check for continuity from terminal B10 to ground.
  6. If continuity exists, repair short in Blue/Green wire between ECU terminal B10 and distributor. If continuity does not exist, substitute a known good ECU and recheck. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box 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. Using a "T" fitting, connect a hand-held vacuum pump/gauge into vacuum hose between throttle body and MAP sensor (vacuum hose No. 21). Apply vacuum. 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 or 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.
  4. Connect ECU Test Harness between ECU and ECU connector. (Scheme 73) Measure voltage between positive terminal D17 and negative terminal D21. If voltage reading is about 3 volts, go to next step. If voltage is not about 3 volts, replace MAP sensor.
  5. Start engine and let idle. If voltage is not about 1 volt, replace MAP sensor. If voltage reading is about 1 volt, substitute a known good ECU. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box 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. Start engine and warm to normal operating temperature (cooling fan comes on). Turn ignition off. Disconnect 2-wire coolant sensor connector. Measure resistance across sensor terminals.
  3. If resistance is not 200-400 ohms, replace TW sensor. If resistance is within specification, turn ignition switch on. Measure voltage between ground and Yellow/Green wire TW sensor harness. If reading is about 5 volts, go to step 4). If reading is not about 5 volts, go to step 5) for A/T models or step 6) for M/T models.
  4. Measure voltage between Yellow/Green (positive) wire and Green/White (negative) terminals. If reading is about 5 volts, substitute a known good ECU and recheck. If condition is corrected, replace original ECU. If voltage reading is not as specified, repair open Green/White wire between ECU terminal D22 and TW sensor.
  5. Disconnect 22-wire connector from A/T control unit. If voltage is now about 5 volts, replace A/T control unit. If reading is not about 5 volts, repair open or short in Yellow/Green wire between ECU terminal D13, A/T control unit and TW sensor. If wire is okay, substitute a known good ECU and recheck. If condition is corrected, replace original ECU.
  6. Repair open or short in Yellow/Green wire between ECU terminal D13 and TW sensor. If wire is okay, substitute a known good ECU and recheck. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 7. If LED is flashing Code 7, go to next step. If LED is not flashing Code 7, problem is intermittent. Check connectors at throttle angle sensor and related circuits.
  2. Turn ignition off. Disconnect 3-wire connector at throttle position sensor. Turn ignition on. Measure voltage between Yellow/White (positive) and Green/White (negative) terminals. 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. (Scheme 73)
  3. Turn ignition on. Measure voltage between positive terminal D11 and negative terminal D22. Voltage should read.5 volt at closed throttle, and about 4.5 volts at wide open throttle, with a smooth transition between the lower and upper voltage specification as the throttle is depressed.
  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/Black (Prelude) wire between ECU terminal D11 and throttle sensor. On A/T models, go to step 5).
  5. Disconnect 22-wire connector from A/T control unit. If throttle sensor now responds as indicated, replace A/T control unit. If throttle sensor does not respond as indicated, check for open or short in Red/Black wire between ECU terminal D11, throttle angle sensor and A/T control unit.
  6. If voltage reading between Yellow/White (positive) and Green/White (negative) terminals in step 2) was 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 D22 and throttle sensor. If reading is not about 5 volts, turn ignition off.
  7. Connect ECU Test Harness between ECU and ECU connector. Turn ignition on. Measure voltage between positive terminal D20 and negative terminal D22. If voltage is about 5 volts, repair open Yellow/White wire between ECU terminal D20 and throttle sensor. If reading is not about 5 volts, substitute a known good ECU. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box for 10 seconds to reset ECU. Start engine and observe CHECK ENGINE light. If light is off, problem is intermittent. Test drive and check again.
  2. If light is on, turn ignition off. Disconnect 4-wire sensor connector at distributor. Measure resistance between Orange/Blue and White/Blue terminals. If reading is not 700-1000 ohms, replace pulse generator assembly. If reading is within specification, proceed to next step.
  3. Check continuity between ground and Orange/Blue wire terminal. Check continuity between ground and White/Blue wire terminal. If continuity exists, sensor is shorted to ground. Replace pulse generator assembly. If no continuity exists, proceed to next step.
  4. Reconnect sensor connector. Attach ECU Test Harness to main wire harness side only. (Scheme 73) Using an ohmmeter, check resistance between connector B13 and B14 terminals. Resistance should be 700-1000 ohms.
  5. If resistance is not within specification, repair open or short in Orange/Blue and/or White/Blue wire. If resistance is within specification, check for continuity from terminal B13 to ground.
  6. If continuity exists, repair short in Orange/Blue wire between ECU terminal B13 and sensor connector. If continuity does not exist, substitute a known good ECU. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box 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. Turn ignition off. Disconnect 2-wire sensor connector. Measure resistance across sensor terminals. If reading is not 700-1000 ohms, replace CYL sensor assembly. If reading is within specification, proceed to next step.
  3. Check continuity between ground and each sensor terminal. If continuity exists, replace CYL sensor assembly. If no continuity exists, proceed to next step.
  4. Reconnect sensor connector. Attach ECU Test Harness to main wire harness side only. Check resistance between connector terminals B11 and B12. Resistance should be 700-1000 ohms.
  5. If resistance is not within specification, repair open or short in Orange and/or White wires. If resistance is within specification, check continuity between terminal B11 and ground. If continuity is not present, repair open in Orange wire between ECU terminal B11 and CYL sensor connector. If resistance is within specification, substitute a known good ECU and retest. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 10. If LED is flashing Code 10, go to next step. If LED is not flashing Code 10, problem is intermittent. Check connectors at TA sensor and related circuits.
  2. If light is on, 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 within specification, disconnect ohmmeter and turn ignition on. Measure voltage between ground and Red/Yellow wire terminal. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 4).
  3. Measure voltage between Red/White (positive) and Green/White (negative) terminals. If voltage is not about 5 volts, repair open circuit in Green/White wire between ECU terminal D22 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 D15 and TA sensor. If wire is okay, substitute a known good ECU and recheck. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box for 10 seconds to reset ECU. Start engine and warm to normal operating temperature. Road test vehicle for about 10 minutes. Try to keep engine speed in 1700-2500 RPM range. Verify if CHECK ENGINE light is on and if LED is flashing Code 12.1f LED is flashing Code 12, go to next step. If LED is not flashing Code 12, problem is intermittent. Check connectors at EGR valve and related circuits.
  2. With engine at idle, disconnect vacuum hose (No. 16) from EGR valve. Using a hand-held vacuum pump/gauge, test for vacuum. If vacuum is not present, go to step 5). If vacuum is present, go to next step.
  3. Disconnect 4-wire connector from vacuum control box and again check for vacuum. If vacuum is present, check vacuum hose routing for entire EGR system. If hose routing is okay, replace EGR solenoid control valve.
  4. If vacuum was not present, check for short to ground in Red wire between EGR solenoid control valve and ECU terminal A11. If wire is okay, substitute a known good ECU and recheck. If condition is corrected, replace original ECU.
  5. Move vacuum pump to EGR valve and apply 8 in. Hg to EGR valve. If vacuum does not hold, and engine does not stall, replace faulty EGR valve or clean blocked EGR passages.
  6. If vacuum held and engine stalled in step 5), disconnect 4-wire connector from control box. Measure voltage between Black/Yellow (positive) terminal on main wire harness and ground. Battery voltage should be present. If battery voltage is not present, repair open in Black/Yellow wire between solenoid valve and fuse No. 12 (Prelude). If battery voltage is present, go to next step.
  7. Reconnect vacuum pump/gauge to EGR vacuum hose (No. 16). Start engine and let idle. Supply battery voltage to Black/Yellow wire terminal of box and ground to Red wire terminal of box. Reading at EGR valve hose should be about 8 in. Hg after one second. If reading is okay, go to step 10). If not, go to step 8).
  8. Turn ignition off. Inspect hoses No. 16 and 24 for leaks, restrictions and misrouting. If problem is found, repair as necessary. If hoses are okay, disconnect lower hose on EGR control solenoid valve and connect a vacuum gauge.
  9. Start engine and allow to idle. If 6-10 in. Hg is not present, replace Constant Vacuum Control Valve (CVC). If 6-10 in. Hg is present, replace EGR control solenoid valve.
  10. If gauge read 8 in. Hg in step 7), turn ignition off and reconnect 4-pin connector. Connect Test Harness (07LAJ-ML80100 ) to EGR lift sensor harness. Turn ignition on. Measure voltage between Red (positive) and Green (negative) wire terminals. If about 5 volts is not present, repair open in Yellow/White wire between ECU terminal D20 and EGR valve or Green/White wire between ECU terminal D22 and EGR valve.
  11. If 5 volts is present, measure voltage between White (positive) and Green (negative) wire terminals. If approximately 1.2 volts is not present, replace EGR valve. Repair short in White/Black or Yellow wire between ECU terminal D12 and EGR lift sensor. If wire is okay, substitute a known good ECU. If proper voltage is present, replace original ECU.
  12. If 1.2 volts is present, observe voltmeter and slowly apply a continuous 8 in. Hg to valve. Repeat several times, fully releasing vacuum between checks. If the maximum voltage is not 4 volts, replace EGR valve. If maximum voltage is 4 volts, ensure voltage consistently increases and decreases as vacuum increases and decreases.
  13. If voltage does not increase and decrease with vacuum, replace EGR valve. If voltage does increase and decrease, reconnect hose No. 16 to EGR valve. Turn ignition off. Connect ECU Test Harness to ECU. (Scheme 73) Start engine and allow to idle. Measure voltage between ECU positive terminals D12 and negative terminals D22. If approximately 1.2 volts is not present, repair open in White/Black or Yellow wire between ECU terminal D12 and EGR lift sensor.
  14. If 1.2 volts are present, connect jumper between terminals A11 and A26. If engine did not stall, repair open in Pink wire between ECU terminal A11 and EGR control solenoid valve. If engine stalled, substitute a known good ECU. If condition goes away, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box 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, go to next step. If LED is not flashing Code 13, problem is intermittent. Test drive may be necessary.
  2. If light is on, turn ignition off. Substitute a known good ECU and recheck. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse in the underhood relay box for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 14. If LED is flashing Code 14, go to next step. If LED is not flashing Code 14, problem is intermittent. Check connectors at EACV and related circuits.
  2. Turn ignition off. Disconnect Electronic Air Control Valve (EACV) connector. Check resistance between the 2 connector terminals on valve.
  3. Resistance should be 8-15 ohms. If 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 Yellow/Black wire terminal and negative Blue/Red wire 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 does exist, repair short in Blue/Red wire between ECU terminal A9 and EACV.
  6. If no battery voltage existed in step 5), measure voltage between ground and Yellow/Black (Prelude) wire terminal. If battery voltage now exists, proceed to step 7). If battery voltage still does not exist, repair open Yellow/Black 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 positive terminals A9 and negative terminals A23. If voltage does not exist, repair open in Black/Blue (Prelude) wire between ECU terminal A9 and EACV.
  8. If battery voltage exists, connect and disconnect terminal A9 to A23. 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.
  1. Turn off ignition. Reset ECU by removing CLOCK fuse in under-hood relay box for 10 seconds. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 15. If LED is flashing Code 15, go to next step. If LED is not flashing Code 15, problem is intermittent. Check connector at distributor and related circuits.
  2. Turn ignition off. Disconnect 6-wire connector at ignitor. 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. (Scheme 73) Turn ignition on. Individually, measure voltage between negative terminal A26 and positive terminals A21 and A22.
  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 Yellow/Green wire between distributor and ECU terminals A21, A22. If wires are okay, replace ignitor unit.
  5. Turn ignition off. Disconnect 6-wire ignitor connector and connectors from ECU side only. Check for continuity between White wires and ECU terminals B15 and B17 and ignitor. If continuity does not exist, repair as necessary. If continuity does exist, check for continuity between ground and White wires of 6-wire connector. If continuity exists, repair short to ground. If continuity does not exist, replace ignitor unit.
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box 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 Hashing Code 16, problem is intermittent. Check connectors at injectors, injector resistor and related circuits.
  2. Using a stethoscope, 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.
  3. Turn ignition off. If engine does not start, check resistance of all injectors. If engine does start, check resistance of injectors which did not click. 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.
  4. If battery voltage is not present, go to step 6). If battery voltage is present, reconnect injector connector(s). Turn ignition off. Connect ECU Test Harness between ECU and ECU connector. (Scheme 73) Turn ignition on. Measure voltage between negative terminal A23 and the following positive terminals. Injector No. 1 - A1 Injector No. 2 - A3 Injector No. 3 - A5 Injector No. 4 - A7
  5. If battery voltage is not present, repair open in wire A1 (injector 1), A3 (injector 2), A5 (injector 3) or A7 (injector 4) between ECU and injector. If battery voltage is present, substitute a known good ECU. If condition is corrected, replace original ECU.
  6. 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.

Engine Will Not Start

  1. Remove HAZARD fuse in main fuse box for 10 seconds to reset ECU. Crank engine for at least 15 seconds to reproduce trouble code in ECU memory. Verify if CHECK ENGINE light is on and if trouble code(s) is present. If light is not on and trouble codes are not present, perform SPARK test in «BASIC TESTING - FUEL INJECTED»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-basic-testing-fuel-injected) article.
  2. If CHECK ENGINE light is on and LED is flashing Code 16, turn ignition off. Disconnect 2-wire connector from auxiliary injector. Check resistance between the injector terminals. Resistance should be 6-10 ohms. If resistance is not 6-10 ohms, replace auxiliary injector.
  3. If resistance was okay, turn ignition switch on. Measure voltage between auxiliary injector connector Yellow wire and ground. If about 10 volts is present, go to step 4). If about 10 volts are not present, 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 retest. If specified voltage is now available, replace original ECU.
  4. Disconnect 2-wire connector from main injector. Measure voltage between main injector's Red wire and ground. If about 10 volts is present, go to step 5). If about 10 volts are not present, repair open or short in Red wire between main injector and ECU terminals A5 and A7. If wire is okay, substitute a known good ECU and retest. If specified voltage is now present, replace original ECU.
  5. Turn ignition off. Connect voltmeter positive lead to Yellow/Black wire of auxiliary injector and voltmeter negative lead to ground. Turn ignition on. If battery voltage is present for 2 seconds, substitute a known good ECU and retest. If specified voltage is now present, replace original ECU. If battery voltage is not present for 2 seconds, go to step 6).
  6. Turn ignition off. Connect ECU Test Harness between ECU and ECU connector. (Scheme 73) Jumper ECU terminals A18, A12 and A14 to each other. Turn ignition on. Check for battery voltage at Yellow/Black wire of auxiliary injector connector.
  7. If battery voltage is not present, check and repair open in Black/Yellow wire between auxiliary injector and main relay or Green/Black wire between main relay and ECU terminals A12 and A14. If wires are okay, replace main relay.
  8. If battery voltage was present from step 6), repair Black wire between ground on thermostat housing and ECU terminals A2 and A4. If wire is okay, substitute a known good ECU and retest. If specified voltage is now present, replace original ECU.
  1. Turn ignition off. Reset ECU by removing CLOCK fuse in under-hood relay box for 10 seconds. Road test vehicle. With transmission in 2nd gear, accelerate to 3500 RPM, then decelerate to 1500 RPM with throttle fully closed. Verify if CHECK ENGINE light is on and if LED is flashing Code 17. If LED is flashing Code 17, go to next step. If LED is not flashing Code 17, problem is intermittent. Check connectors and related circuits.
  2. Block rear wheels and set parking brake. Raise front of vehicle and support with stands. Connect ECU Test Harness between ECU and ECU connector. (Scheme 73) Turn ignition on.
  3. Slowly rotate left front wheel and measure voltage between positive terminal B10 and negative terminal A26. If voltmeter does not pulse, go to step 4). If voltmeter pulses from 0-5 volts, substitute a known good ECU and recheck. If specified voltage is now present, replace original ECU.
  4. Repair open or short in Yellow/Red or White/Blue (Prelude) wire between ECU and VSS. If wire is okay, replace VSS sensor. If voltage is still not as specified, substitute a known good ECU and recheck. If specified voltage is now present, replace original ECU.

Scheme 75

Scheme 75: Prelude 2.1L
Scheme 75: Prelude 2.1L
  1. Turn ignition off. Remove CLOCK fuse in the under-hood relay box for 10 seconds to reset ECU. Start engine. Verify if CHECK ENGINE light is on and if LED is flashing Code 41. If LED is flashing Code 41, go to next step. If LED is not flashing Code 41, problem is intermittent. Check connections at O2 sensor, related circuits and at ECU.
  2. Turn ignition off. Disconnect 4-wire connector from O2 sensor. Measure resistance between connector terminals "A" and "B" on O2 sensor. (Scheme 75) If resistance is 15-20 ohms, go to next step. If resistance is not 15-20 ohms, replace O2 sensor.
  3. Check for continuity from each terminal of O2 sensor to ground. If continuity exists, replace O2 sensor. If continuity did not exist, check for continuity between O2 sensor terminal "A" and terminals "C" and "D" individually. (Scheme 75) If continuity does not exist, go to next step. If continuity did exist, replace O2 sensor.
  4. Measure voltage between positive Yellow/Black terminal and negative Black (Prelude) terminal. If battery voltage does not exist, go to step 6). If battery voltage did exist, disconnect "A" connector at ECU. Measure voltage between positive Yellow/Black terminal and negative Black terminal.
  5. If there is now battery voltage, repair short in Black (Prelude) wire between ECU terminal A6 and O2 sensor. If battery voltage did not exist, substitute a known good ECU. If condition is corrected, replace original ECU.
  6. Measure voltage between Yellow/Black terminal and ground. If battery voltage does not exist, repair open in Yellow/Black wire between O2 sensor and main relay. If battery voltage did exist, turn ignition off. Reconnect 4-wire connector to O2 sensor.
  7. Connect ECU Test Harness connector "Ax to main harness, not ECU. Turn ignition on. Measure voltage between terminal A6 (positive) and A23 (negative). If battery voltage does not exist, repair open in Orange/Black wire between ECU terminal A6 and O2 sensor. If battery voltage did exist, substitute a known good ECU. If condition is corrected, replace original ECU.
  1. Turn ignition off. Remove CLOCK fuse (Prelude) in the under-hood relay box for 10 seconds to reset ECU. Start engine and warm to normal operating temperature (cooling fan comes on). Raise engine speed to 3000 RPM and hold for 2 minutes. Verify if CHECK ENGINE light is on and if LED is flashing Code 43.1f LED is flashing Code 43, go to next step. If LED is not flashing Code 43, problem is intermittent. Check connections at O2 sensor, related circuits and at ECU.
  2. Turn ignition off. Connect ECU Test Harness between ECU and connector. Wait at least 2 minutes with ignition off. Turn ignition on. Measure voltage between terminals D14 (positive) and A26 (negative) as soon as ignition is turned on. If less than .1 volt is present when ignition is first turned on, got to step 4). If more than .1 volt was present, go to next step.
  3. Disconnect 4-wire connector from O2 sensor. Measure voltage at O2 sensor connector between terminal "C" (negative) and "D" (positive). If voltage is more than .1 volt, replace O2 sensor. If voltage was less than .1 volt, repair open in White wire between ECU terminal D14 and O2 sensor.
  4. Disconnect 4-wire connector from O2 sensor. Measure voltage between terminals D14 (positive) and A26 (negative). If voltage is more than .1 volt, replace O2 sensor. If voltage was less than .1 volt, disconnect test connector "D" from main wire harness.
  5. Measure voltage between terminals D14 (positive) and A26 (negative) If voltage is more than .1 volt, repair short in White wire between ECU terminal D14 and O2 sensor. If voltage was less than .1 volt, substitute a known good ECU. If condition is corrected, replace original ECU.

Scheme 76

Scheme 76: WIRING DIAGRAM(S)
Scheme 76: WIRING DIAGRAM(S)

SUMMARY

If no hard fault codes are present, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO-START, etc.) or intermittent diagnosis procedures.

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