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Troubleshooting Malfunction Indicator Light

CAUTION: When substituting or replacement of PCM is recommended, see PCM REMOVAL & REPLACEMENT  for important precautions.
  1. Turn ignition switch on and observe Malfunction Indicator Light (MIL). If MIL always comes on and stays on, go to step  11 . If MIL stays on but sometimes works normally, check for following:
    • Intermittent short in Brown wire between PCM harness connector terminal B54 and DLC 16-pin connector terminal No. 9. See Figure or Figure .
    • Intermittent short in Green/Orange wire between PCM harness connector terminal B5 and gauge assembly harness connector "A" terminal A30. See Figure .

    Repair wiring as necessary. If MIL stays off, go to next step. If MIL stays off but sometimes works normally, check for following malfunctions:

    • Loose No. 9 BACK UP LIGHT, INSTRUMENT LIGHT fuse (10-amp) in driver's under-dash fuse/relay box.
    • Loose No. 46 ACG S fuse (15-amp) in under-hood fuse/relay box.
    • Loose No. 1 FUEL PUMP fuse (15-amp) in driver's under-dash fuse/relay box.
    • Intermittent connection between PCM harness connector terminal B5 (Green/Orange wire) and the gauge assembly harness connector "A" terminal A30.
    • Intermittent open in Green/Orange wire between PCM harness connector terminal B5 and gauge assembly harness connector "A" terminal A30.
    • Intermittent short in Yellow/Red wire between PCM harness connector terminal A7, MAP sensor and counter shaft speed sensor.
    • Intermittent short in Yellow/Blue wire between PCM harness connector terminal A27, EGR valve position sensor, main shaft speed sensor, or intake manifold runner control actuator.
    • Intermittent short in Yellow/Black wire between PCM harness connector terminal B43 and the (APP) sensor.
    • Intermittent short in Yellow/White wire between PCM harness connector terminal B29 and the accelerator pedal position (APP) sensor.
    • Intermittent short in Yellow/Blue wire between PCM harness connector terminal B46 and the fuel tank pressure (FTP) sensor.

      For connector views, see CONNECTOR IDENTIFICATION  . See appropriate wiring diagram under ENGINE PERFORMANCE in WIRING DIAGRAMS. Repair as necessary.

  2. Turn ignition switch off, then on. If low oil pressure light is on, go to next step. If low oil pressure light is not on, check for a blown No. 9 BACK UP LIGHT, INSTRUMENT LIGHT fuse (10-amp) in driver's under-dash fuse/relay box. Also check for short or open in wire between No. 9 BACK UP LIGHT, INSTRUMENT LIGHT fuse (10-amp) in driver's under-dash fuse/relay box and gauge assembly.
  3. Attempt to start engine. If engine starts, go to next step. If engine does not start, go to step  5 .
  4. Turn ignition switch off. Disconnect PCM "B" harness connector. Connect fused jumper wire between ground and PCM harness connector terminal B5. Turn ignition switch on. If MIL comes on, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM. If MIL does not come on, check for blown MIL bulb or open in Green/Orange wire between PCM harness connector terminal B5 and gauge assembly harness connector "A" terminal A30.
  5. Turn ignition switch off. Inspect No. 46 ACG S fuse (15-amp) in under-hood fuse/relay box. If fuse is OK, go to next step. If fuse is not good, check for a short in wire between No. 46 ACG S fuse (15-amp) in under-hood fuse/relay box and PGM-FI main relay. Check for a short in wire between PGM-FI main relay and the PCM, injectors, CKP sensors or CMP sensor.
  6. Inspect No. 1 FUEL PUMP fuse (15-amp) in driver's under-dash fuse/relay box. If fuse is OK, go to next step. If fuse is not good, check for a short in wire between No. 1 FUEL PUMP fuse (15-amp) in driver's under-dash fuse/relay box PGM-FI main relay. Check for a short in wire between PGM-FI main relay and the fuel pump. Check for faulty PGM-FI main relay or a faulty fuel pump.
  7. Disconnect PCM "A" harness connector. With both PCM harness connectors disconnected, measure continuity between ground and terminals A7, A27, B29, B43 and B46 individually. If there is continuity, go to next step. If there is no continuity, go to step  9 .
  8. Disconnect the connector from each of these sensors, one at a time while checking for continuity between ground and terminals A7, A27, B29, B43 and B46 individually.
    • (A7) (Yellow/Red wire) Countershaft speed sensor
    • (A27) (Yellow/Blue wire) EGR valve position sensor
    • (B46) (Yellow/Blue wire) Fuel Tank Pressure (FTP) sensor
    • (A27) (Yellow/Blue wire) Mainshaft speed sensor
    • (A7) (Yellow/Red wire) Manifold Absolute Pressure (MAP) sensor
    • (B29) (Yellow/White wire) APP sensor

    If there is continuity, repair short to ground in wire between PCM and the sensor with the problem wire. If there is no continuity, replace the sensor that made continuity to ground go away when disconnected.

  9. Disconnect the injectors, CKP sensors and CMP sensor connectors, Turn ignition switch on. Measure voltage between ground and PCM harness connector terminal A18. If there is battery voltage, go to next step . If there is not battery voltage, check for an open in wire between PGM-FI main relay and PCM connector terminal A18. Check for poor connection at PGM-FI main relay. Check for faulty PGM-FI main relay. See appropriate wiring diagram under ENGINE PERFORMANCE in WIRING DIAGRAMS. If necessary repair or replace the part.
  10. Check for continuity between ground and PCM harness connector terminals A39, A30 and A73. If there is continuity, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM. If there is not continuity, repair open in wires between ground (G101) and PCM harness connector terminals A39, A30 and A73.
  11. Turn ignition off. Reconnect PCM harness connectors. Turn ignition on. Measure voltage between ground and DLC connector terminal No.9 (Brown wire). If there is about 5 volts, go to step  13 . If there is not about 5 volts, go to next step.
  12. Turn ignition off. Disconnect PCM harness connector "B". Check for continuity between ground and PCM connector terminal B54. If there is continuity, repair short in wire between PCM harness connector terminal B54. If there is not continuity, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM.
  13. Turn ignition off. Disconnect PCM harness connector "A". Turn ignition on. If the MIL stays on, repair short in green/orange wire between gauge assembly harness connector "A" terminal A30 and PCM harness connector terminal B5. If the MIL does not stay on, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM.
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