Alternator Control Circuit Troubleshooting

Connect the Honda Diagnostic System (HDS) to the data link connector (DLC), and check for DTCs. 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. Is there 1 V or less?
YES | - | Go to Step 5 .
NO | - | Go to Step 8 .
Turn the ignition switch OFF, and wait at least 30 seconds. Disconnect engine control module (ECM) connector No. 1 (96P). |

Check for continuity between ECM connector No. 1 terminal No. 80 and body ground. Is there continuity?
YES | - | Repair short in the wire between the alternator and the ECM.■
NO | - | Update the ECM if it does not have the latest software, or substitute a known-good ECM, then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM. ■
Turn the ignition switch OFF, and wait at least 30 seconds. Disconnect ECM connector No. 1 (96P). |

Check for continuity between ECM connector No. 1 terminal No. 80 and alternator 4P connector terminal No. 2. Is there continuity?
YES | - | Replace the alternator or repair the alternator. ■
NO | - | Repair an open in the wire between the alternator and the ECM.■