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Alternator FR Signal Circuit Troubleshooting

  1. Disconnect the alternator 4P connector.
  2. Turn the ignition switch ON (II).
  3. Measure voltage between ECM/PCM connector terminals A24 and B13.
    Fig 1: Measuring Voltage Between ECM/PCM Connector Terminals A24 & B13
    G01475628Courtesy 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 ECM/PCM connector terminals A24 and B13.

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

    1. YES  - The alternator FR signal is OK.
    2. NO  - Go to step 8.
  8. Turn the ignition switch OFF.
  9. Disconnect ECM/PCM connector B (24P).
  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 4-Pin Connector Terminal No. 4 To Body Ground
    G01475629Courtesy of AMERICAN HONDA MOTOR CO., INC.
  12. Check for continuity between body ground and ECM/PCM connector terminal B13.
    Fig 3: Checking Continuity Between Body Ground & ECM/PCM Connector Terminal B13
    G01475630Courtesy 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 ECM/PCM (B13) and the alternator.
  13. Turn the ignition switch OFF.
  14. Disconnect ECM/PCM connector B (24P).
  15. Check for continuity between body ground and ECM/PCM connector terminal B13.
    Fig 4: Checking Continuity Between Body Ground & ECM/PCM Connector Terminal B13
    G01475631Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  - Repair short in the wire between the ECM/PCM (B13) and the alternator.
    2. NO  - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck (see ECM/PCM UPDATING AND SUBSTITUTION FOR TESTING ). If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM.
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