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Malfunction Indicator Light

  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 32-pin harness connector terminal No. 10 and DLC 16-pin connector terminal No. 9. See Figure and Figure .
    • Intermittent open in Gray wire between PCM 32-pin harness connector terminal No. 21 and DLC 16-pin connector terminal No. 7.
    • Intermittent short in Green/Orange wire between PCM 32-pin harness connector terminal No. 18 and gauge assembly 30-pin harness connector terminal No. 30.

    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 on MDX or 7.5-amp on 3.2CL & 3.2TL) 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 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 30-pin harness connector terminal No. 30.
    • Intermittent short in Yellow/Red wire between PCM 31-pin harness connector terminal No. 19, MAP sensor 3-pin harness connector terminal No. 3 and counter shaft speed sensor 3-pin harness connector terminal No. 1.
    • Intermittent short in Yellow/Blue wire between PCM 31-pin harness connector terminal No. 28, TP sensor 3-pin harness connector terminal No. 3, EGR valve lift sensor 3-pin harness connector terminal No. 3, fuel tank pressure sensor 3-pin harness connector terminal No. 1 and main shaft speed sensor 3-pin harness connector terminal No. 1.

      For connector views, see CONNECTOR IDENTIFICATION  . See WIRING DIAGRAMS article. Repair as necessary.

  2. Turn ignition switch off, then on. If oil pressure light is on, go to next step. If oil pressure light is not on, check for a blown No. 9 BACK UP LIGHT, INSTRUMENT LIGHT fuse (10-amp on MDX, 7.5-amp on 3.2CL and 3.2TL) in driver's under-dash fuse/relay box. Also check for short or open in Yellow wire between No. 9 BACK UP LIGHT, INSTRUMENT LIGHT fuse (10-amp on MDX, 7.5-amp on 3.2CL and 3.2TL) in driver's under-dash fuse/relay box and gauge assembly 14-pin harness connector terminal No. 7.
  3. Attempt to start engine. If engine starts, go to next step. If engine does not start, on MDX, go to step  5 . On 3.2CL and 3.2TL, go to step  7 .
  4. Turn ignition switch off. Connect fused jumper wire between ground and PCM 32-pin harness connector terminal No. 18 (Green/Orange wire). 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 32-pin harness connector terminal No. 18 and gauge assembly 30-pin harness connector terminal No. 30.
  5. Check No. 46 ACG S fuse (15-amp) in under-hood fuse/relay box. If fuse is okay, go to next step. If fuse is blown, check for following causes:
    • Short in White/Green wire between No. 46 ACG S fuse (15-amp) in under-hood fuse/relay box 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 fuel injectors, Idle Air Control (IAC) valve or PCM 25-pin harness connector terminals No. 1 and 9.

    Repair as necessary.

  6. Check No. 1 FUEL PUMP fuse (15-amp) in driver's under-dash fuse/relay box. If fuse is okay, go to next step. If fuse is blown, check for following malfunctions:
    • Short in Red/White wire between No. 1 FUEL PUMP fuse (15-amp) in driver's under-dash fuse/relay box and PGM-FI main relay 7-pin harness connector terminal No. 5.
    • Short in Black/Yellow wire between PGM-FI main relay 7-pin harness connector terminal No. 4 and fuel pump 5-pin harness connector terminal No. 5.
    • Faulty PGM-FI main relay or faulty fuel pump.
  7. Turn ignition switch off. Disconnect PCM 31-pin harness connector. Check for continuity between ground and 31-pin harness connector terminals No. 19 (Yellow/Red wire) and 28 (Yellow/Blue wire) individually. If continuity is present, go to next step. If continuity is not present, go to step  9 .
  8. Disconnect harness connectors from each of following sensors one at a time while checking for continuity between ground and PCM 31-pin harness connector terminals 19 (Yellow/Red wire) and 28 (Yellow/Blue wire) individually:
    • Countershaft speed sensor
    • EGR valve lift sensor
    • Fuel Tank Pressure (FTP) sensor
    • Mainshaft speed sensor
    • Manifold Absolute Pressure (MAP) sensor
    • TP sensor

    If continuity is present, repair short in Yellow/Red wire between PCM 31-pin harness connector terminal No. 19 and MAP sensor or countershaft speed sensor or repair short in Yellow/Blue wire between PCM 31-pin harness connector terminal No. 28 and EGR position sensor, FTP sensor, mainshaft speed sensor or TP sensor. See WIRING DIAGRAMS article. If continuity is not present, replace sensor that was disconnected when continuity was no longer present.

  9. Disconnect fuel injector and IAC valve connectors. Turn ignition switch on. Measure voltage between ground and PCM 25-pin harness connector terminals No. 1 and 9 (Yellow/Black wire) individually. If battery voltage is present, go to next step. If battery voltage is not present, check for following problems:
    • Open in Yellow/Black wire between PCM 25-pin harness connector terminals No. 1 and 9 and PGM-FI main relay.
    • Poor connections at PGM-FI main relay.
    • Defective PGM-FI main relay.

    Repair or replace component as necessary.

  10. Turn ignition switch off. Reconnect sensor connectors, then reconnect PCM 31-pin harness connector. Turn ignition switch on. Measure voltage between ground and PCM 25-pin harness connector terminals No. 2 and 10 (Black wire) and terminals No. 20 and 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 in appropriate wiring between ground terminal G101 and PCM 25-pin harness connector terminals No. 2, 10, 20 or 22.
  11. Connect scan tool to DLC. Turn ignition switch on. Check for DTCs. If any DTCs are present, diagnose as directed by DIAGNOSTIC TROUBLE CODE DEFINITIONS  table. If DTCs are not present, turn ignition switch off. Disconnect PCM 32-pin harness connector. Check continuity between ground and 16-pin DLC terminal No. 7 (Gray wire). If continuity is not present, go to next step. If continuity is present, repair short in Gray wire between 16-pin DLC 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 16-pin DLC 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 16-pin DLC terminal No. 7 and PCM 32-pin harness connector terminal No. 21. Check for DTCs. If any DTCs are present, diagnose as directed by DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
  13. Turn ignition switch off, then on. Measure voltage between ground and PCM 32-pin harness connector terminal No. 10 (Brown wire). If about 5 volts are present, go to next step. If about 5 volts are not present, repair short in Brown wire between 16-pin DLC terminal No. 9 and PCM 32-pin harness connector terminal No. 10.
  14. Turn ignition switch off. Disconnect PCM 32-pin harness connector. Turn ignition switch on. If MIL comes on, repair short in Green/Orange wire between PCM 32-pin harness connector terminal No. 18 and gauge assembly 30-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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