How to Tell if You Have a Faulty Alternator

How to Tell if Your Alternator Has Gone Bad

A dead alternator can cause all kinds of headaches, but how can you tell if your alternator is going out before it is too late? When you try to start your car and you hear a clicking sound, that signals your vehicle is dead you are left with several options as to why.

Usually, the problem falls into one of two categories: a dead car battery or a loose battery connection. If the battery is dead, it does not mean this is the only problem you now face. Other causes for a car failing to start are a bad starter or relay. If the starter is good, the last likely culprit is a bad alternator. If the alternator is bad, the battery will most likely be dead as well. So what symptoms can alert you ahead of time that your alternator is going bad?

To know which symptoms indicate you may have a bad alternator, you should first understand what an alternator’s function is. An alternator's job is to generate an electrical charge to recharge your battery as your vehicle depletes the electrical charge the battery carries. Without recharging, eventually all of the electrical systems inside the vehicle will stop working. Alternators fail for a variety of reasons, but driving for long periods of time in hot weather is often the culprit.

Another problem is a bad diode inside of the alternator. Diodes are essential to the charging process, and if they begin to fail, the alternator will quickly go bad. So what can you do to determine if your alternator is going bad before it is completely dead?

Car Battery or Alternator? Learn How to Tell The Difference.

Two of the easiest methods to determine if your alternator is dying are the headlight test and the battery test. The headlight test is quick and easy, and should be performed outdoors to ensure that you don't have a carbon monoxide buildup inside your garage. To perform the headlight test, start your car and turn on your headlights. With the vehicle in park, press on the accelerator while a second person observes the headlights. If the headlights flicker, dim or get brighter when the accelerator is pressed down, your alternator may be bad. No change in headlight brightness indicates that your alternator is likely fine.

A battery test is easy to perform and can be done at home. First, open the hood and start the car. While the engine is running, remove the negative cable from the battery. If the vehicle stalls or dies, the alternator is likely bad. This happens because the alternator is not generating enough electricity to keep the engine running on its own. If the car continues to the run, the problem may lie with the battery.

Unfortunately, there is only one way to know for certain if your alternator is bad, and that is to have it tested. Most service stations can test an alternator, but they will charge you for the labor. Many auto parts stores will test alternators, starters and batteries for free, though you will have to remove the alternator to have it tested at an auto parts store. Once connected to a terminal, an alternator should test between 12 and 13.5 volts. Any number less than this means the alternator is probably bad, while a higher number indicates that the alternator is overcharging the battery.