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Malfunction Indicator Light

  1. Turn ignition 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 the following:
    • Intermittent short in Brown wire between PCM 32-pin harness connector terminal No. 10 and DLC 16-pin connector. See Figure
    • Intermittent open in Gray wire between PCM 32-pin harness connector terminal No. 21 and DLC 16-pin connector.
    • Intermittent short in Green/Orange wire between PCM 32-pin harness connector terminal No. 18 and gauge assembly.

    Repair wiring as necessary. If MIL stays off, go to step  3. If MIL stays off but sometimes works normally, go to next step.

  2. Check for following malfunctions:
    • Loose fuse No. 9 (10-amp on MDX or 7.5-amp on 3.2CL & 3.2TL) in underdash fuse/relay box.
    • Loose fuse No. 46 (20-amp on MDX or 15-amp on 3.2CL & 3.2TL) in underhood fuse/relay box.
    • Loose fuse No. 1 (15-amp) in underdash fuse/relay box.
    • Intermittent connection at PCM 32-pin harness connector terminal No. 18 (Green/Orange wire).
    • Intermittent open in Green/Orange wire between PCM 32-pin harness connector terminal No. 18 and gauge assembly.
    • Intermittent short in Yellow/Red wire between PCM 31-pin harness connector terminal No. 19, MAP sensor and counter shaft speed sensor.
    • Intermittent short in Yellow/Blue wire between PCM 31-pin harness connector terminal No. 28, TP sensor, EGR valve lift sensor, fuel tank pressure sensor and main shaft speed sensor.

    See WIRING DIAGRAMS article. Repair as necessary.

  3. Turn ignition off, then on. If oil pressure light is on, go to next step. If oil pressure light is not on, check for a blown fuse No. 9 (10-amp on MDX, 7.5-amp on 3.2CL and 3.2TL) in underdash fuse/relay box. Also check for short or open in Yellow wire between fuse No. 9 (10-amp on MDX, 7.5-amp on 3.2CL and 3.2TL) in underdash fuse/relay box and gauge assembly 25-pin harness connector.
  4. Attempt to start engine. If engine does not start, go to next step. If engine starts, turn ignition off. Connect fused jumper wire between PCM 32-pin harness connector terminal No. 18 (Green/Orange wire) and ground. Turn ignition 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 32-pin harness connector terminal No. 18 and gauge assembly 32-pin harness connector.
  5. Turn ignition off. Inspect fuse No. 46 (20-amp on MDX, 15-amp on 3.2 CL and 3.2TL) in underhood fuse/relay box. If fuse is okay, go to next step. If fuse is not okay, check for following malfunctions:
    • Short in White/Green wire between under-hood fuse/relay box connector terminal No. 17 and PGM-FI main relay 7-pin harness connector terminal No. 7.
    • Short in Yellow/Black wire between PGM-FI main relay 7-pin harness connector terminal No. 6 and PCM 25-pin harness connector terminals No. 1 and No. 9, fuel injector harness connectors terminal No. 1 and IAC valve harness connector terminal No. 2
    • Blown fuse No. 46 (20-amp on MDX, 15-amp on 3.2CL and 3.2TL) in drivers under dash fuse/relay box.
  6. Check fuse No. 1 (15-amp) in drivers under dash fuse/relay box. If fuse is okay, go to next step. If fuse is not okay, check for following malfunctions:
    • Blown fuse No. 1 (15-amp) in drivers under dash fuse/relay box.
    • Short in Red/White wire between drivers under dash fuse/relay box connector terminal No. 1 and PGM-FI main relay 7-pin harness connector terminal No. 5.
    • Short in Red/Orange wire between PGM-FI relay 7-pin harness connector terminal No. 4 and fuel pump harness connector terminal No. 5.
    • Faulty PGM-FI main relay or faulty fuel pump.
  7. Disconnect PCM 31-pin harness connector. Check for continuity between terminal No. 19 (Yellow/Red wire) and ground and between PCM 31-pin harness connector terminal No. 28 (Yellow/Blue wire) and ground. If continuity is not present in either circuit, go to step  9. If continuity is present in both circuits, go to next step.
  8. While checking for continuity to ground between PCM 31-pin harness connector terminal No. 19 (Yellow/Red wire) or PCM 31-pin harness connector terminal No. 28 (Yellow/Blue wire), disconnect each of following 3-pin connector from sensors one at a time to locate short to ground:
    • Countershaft speed sensor
    • EGR valve lift sensor
    • Fuel tank sensor
    • Main shaft speed sensor
    • MAP sensor
    • TP sensor

    When continuity no longer exists, replace shorted sensor in affected circuit(s). If continuity is still present, locate and repair short to ground in affected circuit. See WIRING DIAGRAMS article. Repair as necessary.

  9. Disconnect fuel injector and IAC valve connectors. Turn ignition on. Measure voltage between ground and PCM 25-pin harness connector terminals No. 1 and No. 9 (Yellow/Black wire). If battery voltage is present, go to next step. If battery voltage is not present, check for an open or poor connection between PCM 25-pin harness connector terminals No. 1 and No. 9 (Yellow/Black wires) and PGM-FI main relay, or defective PGM-FI main relay. Repair as necessary.
  10. Turn ignition off. Reconnect sensor connectors, then reconnect PCM 31-pin harness connector. Turn ignition on. Measure voltage between ground and PCM 25-pin harness connector terminals No. 2 and No. 10 (Black wire) and terminals No. 20 and No. 22 (Brown/Yellow wire). If less than one volt is present, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM. If one volt or more is present, repair open circuit(s) in appropriate wiring between ground and PCM.
  11. Turn ignition off. Connect scan tool to DLC. Turn ignition on. Check for DTCs. If any DTCs are present, diagnose as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If DTCs are not present, turn ignition off. Disconnect PCM 32-pin harness connector. Check continuity between ground and DLC 16-pin connector terminal No. 7 (Gray wire). If continuity is not present, go to next step. If continuity is present, repair short in Gray wire between DLC 16-pin connector terminal No. 7 and PCM 32-pin harness connector terminal No. 21.
  12. Check for continuity in Gray wire between PCM 32-pin harness connector terminal No. 21 and DLC 16-pin connector terminal No. 7. If continuity is present, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM. If continuity is not present, repair open in Gray wire between DLC 16-pin connector terminal No. 7 and PCM 32-pin harness connector terminal No. 21. Check for DTCs. If any DTCs are present, diagnose as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  13. Turn ignition off, then on. Measure voltage between PCM 32-pin harness connector terminal No. 10 (Brown wire) and ground. If about 5 volts are present, go to next step. If about 5 volts are not present, repair short in Brown wire between DLC 16-pin connector terminal No. 9 and PCM 32-pin harness connector terminal No. 10.
  14. Turn ignition off. Disconnect PCM 32-pin harness connector. Turn ignition on. If MIL comes on, repair short in Green/Orange wire between PCM 32-pin harness connector terminal No. 18 and gauge assembly 32-pin harness connector terminal No. 30. If MIL does not come on, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM.
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