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
- Remove the engine compartment covers (see ENGINE COMPARTMENT COVER REPLACEMENT ).
- Connect the HDS to the DLC (see HOW TO USE THE HDS (HONDA DIAGNOSTIC SYSTEM) ).
- Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
- Make sure the HDS communicates with the vehicle and the ECM/PCM. If it does not communicate, 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.
- 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 No. 2 And Positive Terminal Of Battery
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there less than 1 V?
YES - Go to step 12.
NO - Go to step 9.
- Jump the SCS line with the HDS, then turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.NOTE: This step must be done to protect the ECM/PCM from damage.
- Disconnect ECM/PCM connector C (49P).
- Check for continuity between ECM/PCM connector terminal C43 and body ground.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
YES - Repair a short to ground in the wire between alternator 4P connector terminal No. 2 and ECM/PCM connector terminal C43. ■
NO - Update the ECM/PCM if it does not have the latest software (see ECM/PCM UPDATE ), 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 to LOCK (0), or press the engine start/stop button to select the OFF mode.NOTE: This step must be done to protect the ECM/PCM from damage.
- Disconnect ECM/PCM connector C (49P).
- Check for loose terminals and connectors, then check for continuity between ECM/PCM connector terminal C43 and alternator 4P connector terminal No. 2.Fig 3: Checking Continuity Between ECM/PCM Connector Terminal C43 And Alternator 4P Connector Terminal No. 2
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
YES - Replace the alternator , or repair the alternator . ■
NO - Repair an open in the wire between alternator 4P connector terminal No. 2 and ECM/PCM connector terminal C43. ■
- Install the engine compartment covers (see ENGINE COMPARTMENT COVER REPLACEMENT ).
Use the Manual With the Right Hardware
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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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