6 Symptoms of a Bad Alternator

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You approach your vehicle with your mind on where you want to go, but when you turn the ignition key, instead of firing up the engine, all you get are rapid clicks. The first thought that crosses your mind will probably be “my battery is dead,” is it really dead, or is the issue more complicated than that?

Many people, including professionals, are quick to assume a dead battery is a reason a car won’t start, but the same situation could play out with a new battery if you fail to notice the signs and symptoms of a bad alternator, a costly assumption that can make you waste money on multiple batteries in a short duration. Here are 6 symptoms of a bad alternator, and your battery might follow too.

How An Alternator Works

The alternator is the component that satisfies the vehicle’s endless power demands. It takes a lot of power to start the engine and power all the electrical devices and components in a vehicle. Though car batteries have enormous capacities, in the long run, the computers and sensors, heater, GPS, headlights, and others would completely drain the battery of power.

Whenever you start the engine, the alternator quickly takes over the job of supplying power from the battery. It converts the mechanical energy from the engine and converts that into a current which is then used to charge the battery and power the car.

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The parts that make up the alternator such as the rotor, brushes, wires, and other internal parts all wear out over time, reading the signs and knowing when to do so is something everyone should know.

Bad Alternator Symptoms:

6 Symptoms of a Bad Alternator [with Tutorials]

Dim lights

One of the first signs of a failing alternator most drivers seem to recognize is the dim and flickering lights. This is most obvious at night when the headlights are on but also noticeable in the center dome and dash light.

If you notice that these lights grow brighter and dimmer as you increase and decrease the speed of your engine, this is a red flag and a strong indication that your alternator can no longer generate adequate power for the electrical system. An alternator that is working properly will maintain a steady brightness irrespective of what your speed is.

Service engine light

Another obvious sign that something is wrong is when your vehicle shows you “the light”. This signal light varies by model, but when the performance of the alternator starts to dip, the “Check Engine”, “ALT”, or a battery icon indicator will show up in the dash.

Odd noises

An alternator has lots of moving parts that help it convert mechanical to electrical energy. Should one of these parts malfunctions or break off, you’ll likely hear some unusual sounds. Most drivers just assume the noise will clear out when the car starts moving, and sometimes it does, but the noise could indicate that the alternator is going bad, or the serpentine belt which spins the alternator could have stretched and might not be spinning the alternator effectively, resulting in a squealing noise.

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Electrical issues

When the alternator starts failing, other systems that depend on the alternator such as power seats or windows, power locks, air conditioning, dashboard lights, even your car radio may start to act up. Without optimal power, some of these components or devices will not function or will suddenly stop working without any reason, like the radio turning off. The problem might be from something other than the alternator, but it’s worth getting your vehicle checked by a professional if you’re experiencing these sorts of issues.

Engine stalling

Your vehicle may be powered by gasoline, but it also runs on electricity even though it might not be a hybrid. How the engine works with the alternator is simple. The alternator, other than powering the radio, headlights, and others, also provides power to the fuel injection system and spark plugs for the purpose of igniting the gasoline in your engine, and the engine, in turn, spins the alternator.

When the alternator starts malfunctioning, it might not be generating enough power for the fuel injection and spark plugs to keep the engine alive, which might cause problems starting the engine or make it stall for no reason. You’ll notice this often when you take your foot off the gas while waiting for the traffic light or when idling in the garage.

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Dead battery

Batteries are expected to fail, at some point, but a bad alternator can help hasten the process. Without a functioning alternator, the power demands of the vehicle quickly use up all of the battery’s reserves.

Pop the hood and inspect the battery, you’ll think you found the culprit, but a new battery and days later you’re back where you started. If you’re seeing signs of a dead battery, consider checking the alternator before changing the battery.

How to Diagnose a Failing Alternator

What you’ll need to test your alternator are a multimeter, code reader (optional), safety glasses.

If you get a “Check Engine” light, connect the code reader to the diagnostic port and take the reading. Though the codes vary by vehicle make, model, and year, if you get code P0562, you’re likely dealing with a failing alternator and should get it checked out before it fails completely or damages your battery.

If you think the alternator is bad but the warning light is yet to come on, pop the hood and inspect the serpentine belt. If it looks glazed and slightly burned, that’s an indication that the belt is slipping. It means the belt is too loose, so instead of spinning the alternator, it slips around it.

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The friction between metal and rubber heats up the belt, quickly wearing it out. Adjust the tensioner so the belt is firm and tight, but not too tight as that could damage the alternator bearings. Alternatively, you could replace the serpentine belt since it’s quite affordable and easy to install.

Grab your multimeter if everything looks good under the hood. Make sure the vehicle is parked on a level place, engage the parking brake and put on your safety glasses. Set the meter to 20V DC and connect the pins to your battery terminals. A healthy battery should read around 12.5 volts.

Now, start the engine and check the meter reading again. If the alternator is healthy and is charging the battery, this time you should be seeing at least 14.3 volts on the multimeter. If the voltage is within the expected range, load up the electrical system. Turn on the headlights, radio, heater, interior lights, and any other electrical load then check the meter again. You should still get a reading above 13 volts.

If any of the voltages are below the expected value, it’s a strong case to get your alternator checked and possibly replaced.

Q & A

Can A Bad Alternator Ruin a Battery?

A faulty alternator will either kill your battery by not supplying enough charge or by feeding it more than it can handle.

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How Long Will Alternators Last?

On average, an alternator will last about 100,000 to 150,000 miles. Numerous factors affect its performance and lifespan, including how many electrical devices the car has, the conditions in which the vehicle is driven, and the quality of parts used in the electrical components.

What Causes a Faulty Alternator?

Most alternator failure is caused by bad diodes. The diodes are part of an assembly that converts the AC output to a DC supply the vehicle can use. Due to how they are designed, these diodes get warmer as the charging load increases.

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