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CHECK ENGINE Light Stays On

  1. Check ECU for fault codes. See RETRIEVING CODES  . Service codes as necessary. If no codes are present, remove jumper wire from self-diagnostic connector. Start engine. If engine does not start, go to step 6). If engine starts, turn ignition off. Connect ECU Test Harness (07LAJ-PT3010A ) between ECU and ECU connector. See Figure .
  2. Turn ignition on. Measure voltage between terminals C9 (+) and A26 (-) of ECU connector. If about 5 volts are present, go to next step. If about 5 volts are not present, repair short to body ground in White wire between terminal C9 at ECU and self-diagnostic connector.
  3. If about 5 volts are present, connect jumper wire to self-diagnostic connector. If about 5 volts are now present, check for open in White and Black wires between self-diagnostic connector and ECU.
  4. If about 5 volts are still not present, remove jumper wire from self-diagnostic connector. Turn ignition off. Disconnect connector "A" of ECU. Turn ignition on. If CHECK ENGINE light is on, repair short to ground in Blue wire between terminal A13 and combination meter. See Figure .
  5. If CHECK ENGINE light is not on, substitute a known good ECU, and recheck. If system works properly, replace original ECU.
  6. If engine does not start, check fuses No. 5 and IG COIL in underdash fuse box. Replace any bad fuse(s). Turn ignition on. Install jumper wire between self-diagnostic connector terminals. Individually disconnect 3-pin connectors on ignition timing adjuster and MAP, throttle angle sensor and EGR position sensor.
  7. If CHECK ENGINE light goes out, replace sensor causing CHECK ENGINE light to go out. If CHECK ENGINE light is on, connect jumper wire to self-diagnostic connector. Disconnect throttle angle sensor or ignition timing adjuster connector. Check to see if ECU flashes Code 7 or 18. If Code 7 is indicated, replace throttle angle sensor. If Code 18 is indicated, replace ignition timing adjuster.
  8. If Code 7 or 18 is not indicated, turn ignition off. Remove diagnostic jumper wire. Connect ECU Test Harness (07LAJ-PT3010A ) between ECU and ECU connector. See Figure . Disconnect connector "D" from ECU side only. Individually check for continuity between body ground and terminals D19 and D20.
  9. If continuity exists, repair short to ground in Yellow/White wire between ECU terminals D19 or D20 and MAP sensor, ignition timing adjuster, throttle angle sensor or EGR lift sensor.
  10. If continuity does not exist, reconnect connector "D". Reconnect all sensor connectors. Turn ignition on. Individually measure voltage between ECU terminal A26 (-) and terminals C1 (+) and A25 (+). See Figure . If battery voltage is not present, repair open in Yellow/Black wire circuit between main relay and ECU terminals A25 and C1. If circuit is okay, check main relay and connector. If battery voltage is present, turn ignition off. Substitute a known good ECU. If problem goes away, replace original ECU.
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