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Power Outage: How to Spot a Broken Alternator


The first thing most people think about when it comes to automotive charging and electrical systems is the battery. In reality, the battery is responsible for getting the engine started and can get you a little way on reserve, but it’s nothing without the alternator. Alternators not only recharge and maintain battery voltage, but they also supply the power needed for a running engine. A broken alternator can be a real headache, and because it works so closely with the battery, it can be difficult to pinpoint as the culprit for power problems. Luckily, there are some telltale signs that help make a proper diagnosis.

Warning Lights

This is such a straightforward sign that it’s an actual sign. Some cars have dashboard warning lights that say “Alt” or “Gen” (for generator). If either of these lights up, get it checked out, even if there are no other symptoms. Other designs are less discerning and might simply give you a battery warning light. This requires more investigation, as it doesn’t necessarily mean the alternator has a problem, but it doesn’t always mean the battery has a problem, either. If your car warns you about something, though, it’s best to look into it.

Ghost Lights and Accessories

How to Spot a Broken AlternatorOnce the engine’s running, the alternator is responsible for providing energy to the lights, power windows, power locks, the radio and most of your vehicle’s other accessories. Lights are the easiest to notice. If the car is running, but the headlights are dim, or if they flicker when you rev the engine, this could mean they aren’t getting the necessary power from the alternator.

Battery Problems

Alternators can manifest problems that look like it’s the battery’s fault. While a broken alternator can wear out a battery faster, you should always make sure you address the source of the problem. It takes 20 minutes or so of driving for the alternator to recharge the battery. After that, the alternator is completely focused on running the car. If you’ve been driving for that long and the car stalls or loses power, you might have an alternator problem. If you repeatedly can’t start your vehicle that has a new or otherwise good battery, then the alternator could be to blame.

Your Other Senses

Weird sounds under the hood? Unusual smells? If a part of the alternator has broken off internally (a bearing, for instance), it could cause a grinding sound. If an external piece breaks off, it might rattle around in the engine bay. Alternators are belt driven, so if the belt is damaged or worn, it may slip, causing friction and heat. If you smell burning rubber coming from the area, check the belt for tightness, alignment and wear.

Alternators have lifespans just like any other component, and that varies based on the manufacturer. Diodes blow, brushes wear, bearings break, essentially, things happen. If the problem is with the alternator itself, it’s usually replaced entirely. Assuming it’s on top of the engine, it’s pretty easy to remove and replace. Be sure not to replace your alternator over a worn belt. Just make sure your diagnosis is correct, and you’re addressing the root of the problem. If you’re still uncertain, seek a professional’s opinion.

Check out all the electrical system products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on diagnosing a broken alternator, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

Blair Lampe View All


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