2000 Honda S2000FACTORY OEM SERVICE PROCEDURE

Alternator FR Signal Circuit Troubleshooting

  1. Disconnect alternator 4P connector.
  2. Turn the ignition switch ON (II).
  3. Measure voltage between ECM connector terminals B20 and C5.
    Fig 1: Measuring Voltage Between ECM Connector Terminals B20 And C5
    G03692739Courtesy 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 speed at 3,000 RPM without load (in neutral) until the radiator fan comes on, then let it idle.
  7. Measure voltage between ECM connector terminals B20 and C5.

    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 connector C (31P).
  10. Disconnect 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
    G03692740Courtesy of AMERICAN HONDA MOTOR CO., INC.
  12. Check for continuity between body ground and ECM connector terminal C5.
    Fig 3: Checking Continuity Between Body Ground And ECM Connector Terminal C5
    G03692741Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES -  Test the alternator (see ALTERNATOR AND REGULATOR CIRCUIT TROUBLESHOOTING ).
    2. NO -  Repair open in the wire between the ECM (C5) and the alternator.
  13. Turn the ignition switch OFF.
  14. Disconnect ECM connector C (31P).
  15. Check for continuity between body ground and ECM connector terminal C5.
    Fig 4: Checking Continuity Between Body Ground And ECM Connector Terminal C5
    G03692742Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES -  Repair short in the wire between the ECM (C5) and the alternator.
    2. NO -  Substitute a known-good ECM (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSES ) and recheck. If the prescribed voltage is now normal, replace the original ECM (see ECM REPLACEMENT ).
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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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