Alternator Control Circuit Troubleshooting

Check for proper operation of the electrical load detector (ELD) by checking the malfunction indicator lamp (MIL) (see GENERAL TROUBLESHOOTING INFORMATION ).
Connect the Honda Diagnostic System (HDS) to the data link connector (DLC) and check for DTCs (see HOW TO USE THE HDS (HONDA DIAGNOSTIC SYSTEM) ). 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 No. 2 And Positive Terminal Of Battery
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there 1 V or less?
1. YES - Go to step 6.
2. NO - Go to step 9.
Jump the SCS line with the HDS, then turn the ignition switch OFF.
NOTE: This step must be done to protect the powertrain control module (PCM) from damage.
Disconnect PCM connector C (44P).
Check for continuity between PCM connector terminal C38 and body ground.

Fig 2: Checking Continuity Between PCM Connector Terminal C38 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Repair a short in the wire between the alternator and the PCM.
2. NO - Update the PCM if it does not have the latest software (see PCM UPDATING AND SUBSTITUTION FOR TESTING ), or substitute a known-good PCM (see HOW TO SUBSTITUTE THE PCM ), then recheck. If the symptom/indication goes away with a known-good PCM, replace the original PCM (see PCM REPLACEMENT ).
Jump the SCS line with the HDS, then turn the ignition switch OFF.
NOTE: This step must be done to protect the powertrain control module (PCM) from damage.
Disconnect PCM connector C (44P).
Check for continuity between PCM connector terminal C38 and alternator 4P connector terminal No. 2.

Fig 3: Checking Continuity Between PCM Connector Terminal C38 And Alternator 4P Connector Terminal No. 2
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Replace the alternator (see ALTERNATOR REMOVAL AND INSTALLATION ) or repair the alternator (see ALTERNATOR OVERHAUL ).
2. NO - Repair an open in the wire between the alternator and the PCM.