Alternator Control Circuit Troubleshooting

Check for proper operation of the electrical load detector (ELD) by checking for a DTC. If a DTC is present, diagnose and repair the cause before continuing with this test.
NOTE: The ELD DTC does not turn on the MIL.
Connect the Honda Diagnostic System (HDS) to the data link connector (DLC), and 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 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 2 And Positive Battery Terminal
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there 1 V or less?
1. YES -Go to step 9.
2. NO -Go to step 6.
Jump the SCS line with the HDS, then turn the ignition switch OFF.
NOTE: This step must be done to protect the engine control module (ECM)/powertrain control module (PCM) from damage.
Disconnect ECM/PCM connector E (31P) (2004-2005 models) or A (31P) (2006 model).
Check for continuity between ECM/PCM connector terminal E24 (2004-2005 models) or A24 (2006 model) and body ground.
2004-2005 models:

Fig 2: Checking Continuity Between ECM/PCM Connector Terminal E24 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

2006 model:

Fig 3: Checking Continuity Between ECM/PCM Connector Terminal A24 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES -Repair a short to body ground in the wire between the alternator and the ECM/PCM (E24 (2004-2005 models) or A24 (2006 model)).
2. NO -Update the ECM/PCM if it does not have the latest software (see HOW TO UPDATE THE ECM/PCM ), 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 ).
Jump the SCS line with the HDS, then turn the ignition switch OFF.
NOTE: This step must be done to protect the engine control module (ECM)/powertrain control module (PCM) from damage.
Disconnect ECM/PCM connector E (31P) (2004-2005 models) or A (31P) (2006 model).
Check for continuity between ECM/PCM connector terminal E24 (2004-2005 models) or A24 (2006 model) and body ground.
2004-2005 models:

Fig 4: Checking Continuity Between ECM/PCM Connector Terminal E24 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

2006 model:

Fig 5: Checking Continuity Between ECM/PCM Connector Terminal A24 And Body Ground
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 ECM/PCM (E24 (2004-2005 models) or A24 (2006 model)).