How to Identify Automobile Alternator Problems

Electrical systems on modern cars are much more complicated than models from just ten years ago, but all share a few common basics. New or old, a car needs a battery to store electricity and start the engine as well as an alternator to run the electronics in the car and recharge the battery. Although troubleshooting an electrical system can be very difficult, diagnosing alternator problems or ruling them out is a fairly straightforward procedure.

Things You'll Need

• Electrical multimeter
• Battery charger

Instructions

1. Start the car and check for problematic indications on the car's instrument panel. Look for illuminated warning lights that look like a battery, or if the car has an electrical gauge on the dashboard, determine if the needle is in the red low or danger range. If there are no warning signals the electrical charging system, including the battery and alternator, is operating normally.

2. Ensure the battery is not failing by charging or testing the battery. Attach a battery charger to the battery and allow it to charge to full capacity, or take the battery to an auto parts store to be tested (which in most cases is free). If the battery does not fully recharge or fails its testing, it is the source of the electrical problems (not the alternator) and needs to be replaced.

3. Check the alternator voltage. Set the electrical multimeter to measure voltage. Touch the multimeter's red positive lead to the alternator's positive terminal, and touch the multimeter's black negative lead to the car's frame or a common ground. Read the voltage on the multimeter; the alternator should produce at least 14 volts, so a reading of 12 volts or less is indicative of an alternator failure.

References

• Haynes' Automotive Electrical Manual (Haynes Automotive Repair Manual Series No.10420), Haynes, January 1999