2003 Honda Pilot EXFACTORY OEM SERVICE PROCEDURE

Alternator FR Signal Circuit Troubleshooting

  1. Disconnect the alternator 4P connector.
  2. Turn the ignition switch ON (II).
  3. Measure voltage between PCM connector terminals B20 and C5.
    Fig 1: Measuring Voltage Between PCM Connector Terminals B20 & C5
    G01464137Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 5 V? 

    1. YES  -Go to step 4.
    2. NO  -Go to step  13.
  4. Turn the ignition switch OFF.
  5. Reconnect the alternator 4P connector.
  6. Start the engine. Hold the engine at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
  7. Measure voltage between PCM connector terminals B20 and C5.

    Does the voltage decrease when the headlights and rear window defogger are turned on? 

    1. YES  -The ALT FR signal is OK.
    2. NO  -Go to step 8.
  8. Turn the ignition switch OFF.
  9. Disconnect PCM connector C (31P).
  10. Disconnect the alternator 4P connector.
  11. Connect alternator 4P connector terminal No. 4 to body ground with a jumper wire.
    Fig 2: Connecting Alternator 4P Connector Terminal No. 4 To Body Ground With A Jumper Wire
    G01464138Courtesy of AMERICAN HONDA MOTOR CO., INC.
  12. Check for continuity between body ground and PCM connector terminal C5.
    Fig 3: Checking For Continuity Between Body Ground & PCM Connector Terminal C5
    G01464139Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  -Test the alternator (see CHARGING CIRCUIT ).
    2. NO  -Repair open in the wire between the PCM (C5) and the alternator.
  13. Turn the ignition switch OFF.
  14. Disconnect PCM connector C (31P).
  15. Check for continuity between body ground and PCM connector terminal C5.
    Fig 4: Checking For Continuity Between Body Ground & PCM Connector Terminal C5
    G01464140Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  -Repair short in the wire between the PCM (C5) and the alternator.
    2. NO  -Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING ). If voltage is normal, replace the original PCM.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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