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 Control Circuit Troubleshooting
- Connect the Honda Diagnostic System (HDS) to the data link connector (DLC) (see step 2 on GENERAL TROUBLESHOOTING INFORMATION ).
- Turn the ignition switch ON (II).
- Make sure the HDS communicates with the vehicle and the engine control module (ECM)/powertrain control module (PCM). If it doesn't, troubleshoot the DLC circuit (see DLC CIRCUIT TROUBLESHOOTING ).
- Check for DTCs (see GENERAL TROUBLESHOOTING INFORMATION ). If a DTC is present, diagnose and repair the cause before continuing with this test.
- Disconnect the alternator 4P connector from the alternator.
- Start the engine, and turn on the headlights to high beam.
- 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 2 And Positive Terminal Of Battery
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there 1 V or less?
YES -Go to step 11.
NO -Go to step 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.
- Disconnect ECM/PCM connector B (44P).
- Check for continuity between ECM/PCM connector terminal B41 and body ground.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
YES -Repair short in the wire between the alternator and the ECM/PCM.
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 ).
- 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.
- Disconnect ECM/PCM connector B (44P).
- Check for continuity between ECM/PCM connector terminal B41 and alternator 4P connector terminal No. 2.
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.
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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.