Alternator Control Circuit Troubleshooting

WARNING: This page is about a different car, the 2008 Honda Pilot, 2007 Honda Pilot, and 2006 Honda Pilot. However, it is still accessible from the selected car via links, so may be relevant.

Connect the Honda Diagnostic System (HDS) to the data link connector (DLC), and check for DTCs (see step 2 in 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 & Positive Terminal
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there 1 V or less?

YES - Go to step 8.

NO - Go to step 5.
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 For Continuity Between PCM Connector Terminal C38 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES - Repair short in the wire between the alternator and PCM.

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 For Continuity Between PCM Connector Terminal C38 & Alternator 4P Connector Terminal No. 2
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES - Replace the alternator (see ALTERNATOR REMOVAL AND INSTALLATION ), or repair the alternator (see ALTERNATOR OVERHAUL ).

NO - Repair an open in the wire between the alternator and PCM.