2003 Acura MDX BaseFACTORY OEM SERVICE PROCEDURE

Alternator FR Signal Circuit Troubleshooting

  1. Start the engine, and let it idle.
  2. Monitor the ALTERNATOR in the DATA LIST with the HDS.
  3. Check if the indicated percentage is varied when the lighting switch is ON.

    Is the percentage varied? 

    1. YES  - The alternator signal circuit is OK.
    2. NO  - Go to step 4.
  4. Turn the lighting switch and ignition switch OFF.
  5. Disconnect the alternator 4P connector.
  6. Turn the ignition switch ON (II).
  7. Measure voltage between alternator 4P connector terminal No. 4 and body ground.
    Fig 1: Measuring Voltage Between Alternator 4P Connector Terminal No. 4 And Body Ground
    G03639901Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 5 V? 

    1. YES  - Replace the alternator, then go to step  1.
    2. NO  - Go to step 8.
  8. Turn the ignition switch OFF.
  9. Jump the SCS line with the HDS.
  10. Disconnect PCM connector A (73P).
  11. Check for continuity between alternator 4P connector terminal No. 4 and body ground.
    Fig 2: Checking Continuity Between Alternator 4P Connector Terminal No. 4 And Body Ground
    G03639902Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES  - Repair short in the wire between at the alternator connector and the PCM.
    2. NO  - Go to step 12.
  12. Check for continuity between alternator 4P connector terminal No. 4 and PCM connector terminal A25.
    Fig 3: Checking Continuity Between Alternator 4P Connector Terminal No. 4 And PCM Connector Terminal A25
    G03639903Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

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