How to Know When a Alternator Is Bad or Needs to Be Replaced

by Arthur Barnhouse
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The alternator is a key component of your vehicle’s electrical system. While the battery stores electricity and supplies a power source for when the vehicle is turned off, it’s the alternator that continuously recharges the battery as the engine runs. If the alternator malfunctions or dies completely, not only does the car battery fail to charge, your vehicle will stop operating altogether. Therefore, it is essential for you to determine whether your alternator is working correctly or needs to be replaced.

Step 1

Pop the hood and locate the battery. Remove any protective shields or coverings from the battery. It is important that the car is not running, as first you must check only the battery’s voltage to eliminate it as the culprit and establish a baseline.

Step 2

Connect the positive lead of your voltage meter to the positive terminal on the battery (marked with a plus sign). Similarly, connect the negative lead of the meter to the battery’s negative terminal (marked with a minus sign).

Step 3

Look at the readout on your voltage meter. Your meter should show a reading of approximately 12.5 to 12.8 volts. Remember, the engine should not be running when you take this reading. Also, turn off all electrical accessories (radio, lights, etc.).

Step 4

Start your vehicle and allow it idle. Make sure all electrical accessories are turned off.

Step 5

Connect the positive lead of your voltage meter to the battery’s positive terminal and the negative lead to the negative terminal.

Take note of the reading on your voltage meter. You should see an increase of voltage, anywhere from 13.6 to 14.3 volts (or more on some high-end, performance vehicles). If you fail to see an increase in voltage output, that means the alternator is not producing a charge and is in need of repair or replacement.

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