How to Tell If an Alternator is Going Bad

The alternator in a car engine is, in essence, the generator. The purpose of the alternator is to convert gasoline into energy that can power the electrical components of your car, including replacing energy in the battery. The alternator is essential to keeping the car running for a long time. With a little observation, you can easily tell when an alternator is going bad and have it replaced before it becomes a real problem.

Difficulty: Easy

Instructions

1. Keep an eye on your "battery" or "alternator" light. This light should show up on your dashboard when you start the car (if it doesn't, it may be burned out) but it should not flash on when you are driving. If it does, it is a sure sign there is something failing in your alternator or your battery.

2. Turn on your turn signal. If one is blinking at a slower rate than the other, or if they are blinking at a slower rate than usual, your alternator may be the real culprit. Other signs include the dashboard lights going dim or flickering, the power steering going out (the steering wheel becomes stiff), or dimming headlights.

3. Listen to your engine. A grinding noise coming from the alternator may be a sign the bearings are wearing down. A loud squeal may also be indicative of a failing alternator or a worn alternator belt.

4. Look at your alternator. If you do not know where your alternator is, look at the pulley-configuration chart sticker on the front of your engine. The alternator will be labeled ALT, alternator, or GEN, generator. The alternator will be near the front of the engine. Once you find your alternator, if the belt looks thin or worn, or if there are belt shavings on your alternator, the belt will need to be replaced. It could also be a sign of a failing alternator.

5. Use a voltometer set to a DC scale. Place the red lead on the positive terminal of your battery and the black lead on the negative, or ground. Start the car and turn off all accessories (heat, radio, lights). Rev the engine. The voltage should be around 14 volts. If it is under 12, there is a good chance you have a failed alternator. Turn on all your accessories, and rev the engine again. If the voltometer reads less than 13 volts, there is a good chance your alternator is going bad. Most auto-parts shops are willing to do this for you free of charge.

6. Remove the alternator and have it load-tested. This will be the final and definitive test. If you cannot remove it from your engine and take it to an auto-parts store, you will need a mechanic to perform this test.

Tips & Warnings

• If you have had to jump-start your car several times in the past week to get it going, have the alternator and the battery checked.
• Always be careful when examining an engine while it is running.

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