2002-2004 models

Disconnect the alternator 4P connector.
Turn the ignition switch ON (II).
Measure voltage between ECM/PCM connector terminals A24 and B13.

Fig 1: Measuring Voltage Between ECM/PCM Connector Terminals A24 And B13
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there about 5 V?
1. YES - Go to step 4.
2. NO - Go to step 13.
Turn the ignition switch OFF.
Reconnect the alternator 4P connector.
Start the engine. Hold the engine speed at 3,000 RPM without load (in Park or neutral) until the radiator fan comes on, then let it idle.
Measure voltage between ECM/PCM connector terminals A24 and B13.

Fig 2: Measuring Voltage Between ECM/PCM Connector Terminals A24 And B13
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Does the voltage decrease when the headlights and rear window defogger are turned on?
1. YES - The alternator signal is OK.
2. NO - Go to step 8.
Turn the ignition switch OFF.
Disconnect ECM/PCM connector B (24P).
Disconnect the alternator 4P connector.
Connect alternator 4P connector terminal No. 4 to body ground with a jumper wire.

Fig 3: Connecting Alternator 4P Connector Terminal No 4 To Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.
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?
1. YES - Test the alternator (see CHARGING SYSTEM INDICATOR CIRCUIT TROUBLESHOOTING ).
2. NO - Repair open in the wire between the ECM/PCM (B13) and the alternator.
Turn the ignition switch OFF.
Disconnect ECM/PCM connector B (24P).
Check for continuity between body ground and ECM/PCM connector terminal B13.

Fig 5: Checking Continuity Between Body Ground And ECM/PCM Connector Terminal B13
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Repair short in the wire between the ECM/PCM (B13) and the alternator.
2. NO - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM (see HOW TO UPDATE 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 ).