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Home >> Honda >> 2004 >> Pilot EX >> Repair and Diagnosis >> Engine Performance >> System >> PGM-FI System >> MIL Circuit Troubleshooting
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MIL Circuit Troubleshooting

  1. Connect the scan tool or the HDS to the DLC (see HOW TO USE THE HONDA DIAGNOSTIC SYSTEM (HDS) ).
  2. Turn the ignition switch ON (II), and read the scan tool or the HDS.

    Does the scan tool or the HDS communicate with the PCM? 

    1. YES  -Go to step 3.
    2. NO  -Go to troubleshooting DLC Circuit Troubleshooting (see DLC Circuit Troubleshooting  ).
  3. Check for DTCs with the scan tool or the HDS.

    Are any DTCs indicated? 

    1. YES  -Go to the DTC Troubleshooting Index.
    2. NO  -Go to step 4.
  4. Turn the ignition switch OFF.
  5. Turn the ignition switch ON.

    Does the MIL come on and stay on for more than 20 seconds after turning the ignition switch ON (II)? 

    1. YES  -If the MIL always comes on and stays on, go to step  22. But if the MIL sometimes works normally, first check for these problems:
      • An intermittent short in the wire between the PCM (A10) and the Data Link Connector (DLC) connector.
      • An intermittent short in the wire between the PCM (A10) and the gauge assembly.
    2. NO  -If the MIL is always off, go to step 6. But if the MIL sometimes works normally, first check for these problems.
    • A loose No.9 BACK UP LIGHT, INSTRUMENT LIGHT (10A) fuse in the driver's under-dash fuse/relax box.
    • A loose ACGS (15A) fuse in the under-hood fuse/relax box.
    • A loose No. 1 FUEL PUMP (15A) fuse in the driver's under-dash fuse/relay box.
    • A poor connection at PCM terminal A18.
    • An intermittent open in the PUR wire between the PCM (A18) and the gauge assembly.
    • An intermittent short in the wire between the PCM (C19) and the manifold absolute pressure (MAP) sensor, the countershaft speed sensor.
    • An intermittent short in the wire between the PCM (C28) and the throttle position (TP) sensor, Exhaust Gas Recirculation (EGR) valve position sensor, the mainshaft speed sensor, or the fuel tank pressure (FTP) sensor.
  6. Turn the ignition switch OFF and then ON (II) again.

    Is the low oil pressure indicator on? 

    1. YES  -Go to step 7.
    2. NO  -Check for these problems:
    • A blown No. 9 BACK UP LIGHT, INSTRUMENT LIGHT (10A) fuse in the driver's under-dash fuse/relay box.
    • A short or open in the wire between No. 9 BACK UP LIGHT, INSTRUMENT LIGHT (10A) fuse and the gauge assembly.
  7. Try to start the engine.

    Does the engine start? 

    1. YES  -Go to step 8.
    2. NO  -Go to step  11.
  8. Turn the ignition switch OFF.
  9. Connect PCM connector terminal A18 to body ground with a jumper wire.
    Fig 1: Connecting PCM Connector Terminal A18 To Body Ground With A Jumper Wire
    G01464083Courtesy of AMERICAN HONDA MOTOR CO., INC.
  10. Turn the ignition switch ON (II).

    Is the MIL on? 

    1. YES  -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If the symptom/indication goes away, replace the original PCM.
    2. NO  -Check for an open in the wires between the PCM (A18) and the gauge assembly. Also check for a blown MIL bulb.
  11. Turn the ignition switch OFF.
  12. Inspect the ACGS (15A) fuse in the under-hood fuse/relay box.

    Is the fuse OK? 

    1. YES  -Go to step 13.
    2. NO  -Check for these problems:
    • A short in the wire between the ACGS (15A) fuse and the PGM-FI main relay.
    • A short in the wire between the PGM-FI main relay and the PCM, injectors, or IAC valve.
  13. Inspect the No. 1 FUEL PUMP (15A) fuse in the driver's under-dash fuse/relay box.

    Is the fuse OK? 

    1. YES  -Go to step 14.
    2. NO  -Check for these problems:
    • A short in the wire between the No. 1 FUEL PUMP (15A) fuse and the PGM-FI main relay.
    • A short in the wire between the PGM-FI main relay and the fuel pump.
    • A faulty PGM-FI main relay or a faulty fuel pump.
  14. Disconnect PCM connector C(31P).
  15. Check for continuity between body ground and PCM connector terminals C19 and C28 individually.
    Fig 2: Checking For Continuity Between Body Ground & PCM Connector Terminals C19 & C28
    G01464084Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  -Go to step 16.
    2. NO  -Go to step  17.
  16. Disconnect the 3P connector from each of these sensors, one at a time, and check for continuity between body ground and PCM connector terminal C19 and C28 individually.
    • Manifold Absolute Pressure (MAP) sensor
    • Countershaft speed sensor
    • Exhaust Gas Recirculation (EGR) valve position sensor
    • Throttle Position (TP) sensor
    • Fuel Tank Pressure (FTP) sensor
    • Mainshaft speed sensor
    Fig 3: Checking For Continuity Between Body Ground & PCM Connector Terminal C19 & C28
    G01464085Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  -Repair short to body ground in the wire between PCM (C19) and the MAP sensor or countershaft speed sensor, or PCM (C28) and the TP sensor or FTP sensor.
    2. NO  -Replace the sensor that made continuity to body ground go away when disconnected.
  17. Disconnect the injectors and IAC valve connectors.
  18. Turn the ignition switch ON (II).
  19. Measure voltage between body ground and the PCM connector terminals B1 and B9 individually.
    Fig 4: Measuring Voltage Between Body Ground & The PCM Connector Terminals B1 & B9
    G01464086Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there battery voltage? 

    1. YES  -Go to step 20.
    2. NO  -Check for these problems:
    • An open in the wire(s) between the PGM-FI main relay and PCM connector terminals B1 and B9.
    • Poor connections at the PGM-FI main relay.
    • A faulty PGM-FI main relay (see PGM-FI MAIN RELAY CIRCUIT TROUBLESHOOTING ). If necessary, repair or replace the part.
  20. Reconnect the connectors to the sensors, then reconnect PCM connector C (31P).
  21. Turn the ignition switch ON (II), and measure voltage between body ground and PCM connector terminals B2, B10, B20 and B22 individually.
    Fig 5: Measuring Voltage Between Body Ground & PCM Connector Terminals B2, B10, B20 & B22
    G01464087Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there less than 1.0 V? 

    1. YES  -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING 5). If the symptom/indication goes away, replace the original PCM.
    2. NO  -Repair the open in the wire(s) between G101 and the PCM (B2, B10, B20, B22) that had more than 1.0 V.
  22. Turn the ignition switch OFF, then turn it back ON (II), and measure voltage between PCM connector terminal A 10 and body ground.
    Fig 6: Measuring Voltage Between PCM Connector Terminal A 10 & Body Ground
    G01464088Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 5 V (or battery voltage)? 

    1. YES  -Go to step  26.
    2. NO  -Go to step 23.
  23. Turn the ignition switch OFF.
  24. Disconnect PCM connector A (32P).
  25. Check for continuity between PCM connector terminal A10 and body ground.
    Fig 7: Checking For Continuity Between PCM Connector Terminal A10 & Body Ground
    G01464089Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  -Repair short in the wire between the data link connector and the PCM (A10).
    2. NO  -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If symptom/indication goes away, replace the original PCM.
  26. Turn the ignition switch OFF.
  27. Disconnect PCM connector A (32P).
  28. Turn the ignition switch ON (II).

    Does the MIL stay on? 

    1. YES  -Repair short in the wire between the gauge assembly and the PCM (A18).
    2. NO  -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If the symptom/indication goes away, replace the original PCM.
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