Alternator Output Test

Start engine and allow it to warm to normal operating temperature (cooling fan comes on). Turn ignition switch to OFF position.
Disconnect alternator harness connector. See Figure. Turn ignition switch to ON position. Ensure battery voltage exists between Black/Yellow wire terminal of harness connector and ground. If battery voltage is not present, check for open circuit in Black/Yellow wire between dash fuse box and alternator. If battery voltage is present, go to next step.
Connect voltmeter positive lead to battery positive post and negative lead to White/Yellow wire terminal of harness connector. Start engine and turn off all accessories. If battery voltage is not present, check for open circuit in White/Yellow wire between alternator and engine Electronic Control Unit (ECU). If open circuit is not present, also check for faulty engine ECU. If battery voltage is present, turn on headlights. Voltage should not be present. If battery voltage is present, check for short circuit to ground in White/Yellow wire between alternator and engine ECU. If short circuit to ground is not present, also check for faulty engine ECU. If battery voltage is not, go to next step.
Turn ignition off. Reconnect alternator harness connector. Connect Alternator Tester (Sun VAT-40) with integral carbon pile to system using alternator tester manufacturer's instructions. Set alternator tester switch to position No. 1. Go to next step.
Start engine. Ensure all accessories are off. move tester switch to position No. 2. Remove inductive pick-up, and zero alternator tester ammeter. Reconnect inductive pick-up, ensure arrow on inductive pick-up is pointing away from alternator. Go to next step.

NOTE: Due to engine operation, subtract 5-10 amperes from maximum reading.

Fig 1: Alternator Specification Charts

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Operate engine at 2000 RPM and apply a load with the carbon pile so voltage reading drops to no less than 12 volts. Cooling fans must not come on while testing. Check maximum amperage and compare with alternator specification chart. See Fig 1. If amperage reading is as specified, charging system is okay. If amperage reading is not as specified, go to next step, perform full field test. See FULL FIELD TEST .