how to tell if alternator is bad
You get in your car, turn the key, and then…nothing. If you’ve been there before (and chances are high that you have) you know exactly what happens next. Your stomach sinks and you frantically turn the key again. Instead of sitting in your driveway, apartment lot, or work parking garage in denial, jump into action and find a solution.
The elimination process: what’s causing the problem?
If your car won’t start, it’s often due to a malfunction of either the battery or the alternator. If it’s one of those two, placing the blame can be relatively simple.
Starting and running an engine, in its simplest form, is a three-step process. First, the battery delivers a jolt of electricity to the starter. This starts the engine running, which puts the alternator into action. Finally, the alternator completes this cycle by charging the battery.
Using the process of elimination, find the culprit by bypassing the battery’s role and jump-starting your car. If the engine starts but dies immediately, your alternator probably isn’t keeping your battery charged. If a jump starts and keeps your car running, but the car can’t start again off of its own power, a dead battery is likely your answer.
Confirming the battery is the problem
First, check the dashboard battery gauge. The battery should be giving a charge, even while the vehicle is off. If the dashboard lights are dim, something is likely wrong with your battery. Try turning on your windshield wipers, lights or automatic windows. Then make sure these are all turned off and once again try to start the car.
If it still won’t start, use a rag to carefully wipe away any corrosion on the battery and have someone jump-start it. After running the motor for a while, turn the car off. If you can’t get it to restart, this is a sign the alternator is doing its job of keeping the battery working while the motor is running, but the battery isn’t retaining the charge when the alternator has stopped
As batteries age, they become less able to retain a charge because the metal inside corrodes. Eventually, the level of battery charge diminishes to the point where, no matter how much power the alternator gives to it, the battery can’t hold enough power to start the car. However, there are steps you can take to help preserve your car battery life.
Troubleshooting the alternator
If the above steps reveal that the battery is working, it’s time to take a closer look at the alternator. There are certain signs of a bad alternator to look for:
- While running the car, note the brightness of the interior lights. If the dashboard gradually dims, the alternator is likely at fault.
- Do you notice your headlights running brighter as you accelerate and dimming as you stop? This is often caused by the alternator not keeping the battery adequately charged.
- Did you hear a growling sound before the trouble started? That sometimes occurs before an alternator fails.
- Are there signs your alternator is overheating, such as the smell of burning rubber or hot wires? If so, it’s time to replace it.
- Some may recommend running the engine with the negative battery cable disconnected to test the alternator. However, this is not a good idea because it could damage the electrical system of your vehicle and cause greater problems.
If you notice any of these symptoms, you might need to replace your alternator. Depending on your car, replacing an alternator can be an expensive repair.
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