Top 10 Signs Of Alternator Problems - Auto | HowStuffWorks

Within the instrument cluster of most cars built in the last decade is a warning light dedicated to signaling an alternator issue. In most cases the light is shaped like a battery, though some show "ALT" or "GEN," meaning alternator or generator, respectively.

In some older cars, the alternator is referred to as a generator, which may be helpful to know if you're looking through the owner's manual or a shop manual.

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What Is an Alternator?

The alternator is a relatively simple component containing only a few parts, but it plays a critical role in the operation of any gasoline-powered vehicle. Essentially, the alternator turns the mechanical energy of the engine's rotating crank shaft into electricity through induction. Wires within the alternator cut through a magnetic field; this in turn induces electrical current. That current is used to power your car's electrical system, which can be anything from headlights to the electro-hydraulic lifts on a snow plow. The alternator also keeps the battery fully charged, providing the power it needs to start the car.

Many people see the infamous warning light and instinctively think they have a battery problem, but that's not really why the light goes on.

This light is linked to computer systems within the car monitoring the voltage output of the alternator. If the alternator's output goes below or above a preset limit, then the dash light comes on.

Once the output is within range, the light remains unlit. In the early stages of alternator problems the light can seem to flicker — on for just a second and then off again. Or maybe it lights up only when accessories are activated.

Most alternators have an output between 13 and 14.5 volts that they try to maintain at a constant level. As more power is demanded your car's headlights, the windshield wipers, your radio, the heated seats, the rear window defroster,and so on, the alternator needs to work harder to maintain the necessary voltage.

If your car's alternator is not working to its full potential, or demands are placed on it that it can no longer meet, the voltage will either go above or below the set level and switch on the warning light.