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Alternator Control Circuit Troubleshooting

  1. Connect the Honda Diagnostic System (HDS) to the data link connector (DLC) (see step 2 on HOW TO USE THE HDS (HONDA DIAGNOSTIC SYSTEM) ).
  2. Turn the ignition switch ON (II).
  3. Make sure the HDS communicates with the vehicle and the engine control module (ECM)/powertrain control module (PCM). If it doesn't communicate, troubleshoot the DLC circuit (see DLC CIRCUIT TROUBLESHOOTING (PART 2) ).
  4. Check for DTCs (see GENERAL TROUBLESHOOTING INFORMATION ). If a DTC is present, diagnose and repair the cause before continuing with this test.
  5. Disconnect the alternator 4P connector from the alternator.
  6. Start the engine, and turn on the headlights to high beam.
  7. Measure the voltage between alternator 4P connector terminal No. 2 and the positive terminal of the battery.
    Fig 1: Measuring Voltage Between Alternator 4P Connector Terminal No. 2 And Positive Terminal Of Battery
    G05457455Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there 1 V or less? 

    YES  -Go to step  11.

    NO  -Go to step 8.

  8. Jump the SCS line with the HDS, then turn the ignition switch OFF.
    NOTE: This step must be done to protect the ECM/PCM from damage.
  9. Disconnect ECM/PCM connector A (31P).
  10. Check for continuity between ECM/PCM connector terminal A24 and body ground.
    Fig 2: Checking Continuity Between ECM/PCM Connector Terminal A24 And Body Ground
    G05457456Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    YES  -Repair short to body ground in the wire between the alternator and the ECM/PCM (A24).

    NO  -Update the ECM/PCM if it does not have the latest software (see UPDATING THE ECM/PCM ), or substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM ), then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM (see ECM/PCM REPLACEMENT ).

  11. Jump the SCS line with the HDS, then turn the ignition switch OFF.
    NOTE: This step must be done to protect the ECM/PCM from damage.
  12. Disconnect ECM/PCM connector A (31P).
  13. Check for continuity between ECM/PCM connector terminal A24 and alternator 4P connector terminal No. 2.
    Fig 3: Checking Continuity Between ECM/PCM Connector Terminal A24 And Alternator 4P Connector Terminal No. 2
    G05457457Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    YES  -Replace the alternator (see ALTERNATOR REMOVAL AND INSTALLATION  ) or repair the alternator (see ALTERNATOR OVERHAUL  ).

    NO  -Repair open in the wire between the alternator and the ECM/PCM (A24).

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