Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Alternator FR Signal Circuit Troubleshooting
- Start the engine, and let it idle.
- Monitor the ALTERNATOR in the DATA LIST with the HDS.
- Check if the indicated percentage changes when the headlight switch is turned on.
Does the percentage vary?
YES -The alternator signal circuit is OK.
NO -Go to step 4.
- Turn the headlight switch and ignition switch OFF.
- Jump the SCS line with the HDS.
- Disconnect the alternator 4P connector.
- Disconnect ECM/PCM connector A (31P).
- Check for continuity between body ground and ECM/PCM connector terminal A12.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
YES -Repair short in the wire between the ECM/PCM (A12) and the alternator.
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 ).
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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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