Time: 2 hrs

Difficulty: moderate to difficult 

Cost: $80-150 (brand)

BACKGROUND

After the battery starts the vehicle, all electrical function is power-sourced from the alternator. If the alternator fails, or drops below battery voltage, the battery will supply current until it discharges.

The alternator is the current-generator driven off the vehicle's primary drive belt. It is supplied by battery voltage on startup to excite the internal windings. Once operating, current flows from the alternator to charge the battery and supply the host of vehicle electrical demands. Because engine RPM varies, the output voltage is regulated to an even 13.5-14.5 volts.

REPLACEMENT

If alternator output voltage is less than battery voltage (12.6 volts for a fully charged automotive battery), it likely needs to be replaced. Alternator output can be checked with a voltmeter at the battery.

Watch the video below to see how the alternator was diagnosed and replaced on a 2007 Honda Odyssey.