'04 model

Start the engine, and let it idle.
Monitor the ALTERNATOR in the DATA LIST with the HDS.
Check if the indicated percentage varies when the headlight switch is 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.
Disconnect the alternator 4P connector.
Turn the ignition switch ON (II).
Measure voltage between ECM/PCM connector terminals A9 and B13.

Fig 1: Measuring Voltage Between ECM/PCM Connector Terminals A9 And B13
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there about 5 V?

YES -Go to step 8.

NO -Go to step 13.
Turn the ignition switch OFF.
Jump the SCS line with the HDS.
Disconnect ECM/PCM connector B (24P).
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 Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Check for continuity between body ground and ECM/PCM connector terminal B13.

Fig 3: Checking Continuity Between Body Ground And ECM/PCM Connector Terminal B13
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES -Test the alternator (see ALTERNATOR AND REGULATOR CIRCUIT TROUBLESHOOTING ).

NO -Repair open in the wire between the ECM/PCM (B13) and the alternator.
Turn the ignition switch OFF.
Jump the SCS line with the HDS. :
Disconnect ECM/PCM connector B(24P).
Check for continuity between body ground and ECM/PCM connector terminal B13.

Fig 4: Checking Continuity Between Body Ground And ECM/PCM Connector Terminal B13
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES -Repair short in the wire between the ECM/PCM (B13) 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 ).