How to Check the Alternator


Start the car, and turn off all electrical components, including the radio, heater, dome light, air conditioner and GPS. Turn on the headlights, and make sure they are on the low-beam setting.


Ask someone to stand in front of the car and watch the lights as you rev the engine. If the lights dim when the engine is revved, there may be a problem with the alternator. If they get brighter, the alternator is probably working, but more proof is needed. Turn off the engine.


Pull the hood release mechanism. Locate the safety release under the hood and press it to fully release the hood. Engage the hood-prop mechanism to prevent the hood from crashing down on you while you are inspecting the alternator.


Locate the alternator, and check to make sure that all of the connecting wires are firmly in place. Check the battery connections as well.


Connect the voltage meter to the positive battery terminal. Idle the motor at 2,000 to 3,000 rpm. Read the voltage meter. The meter should read 13.6 to 14.3 volts. If the reading is below 13.6, the alternator needs to be replaced.


Turn off the engine. Disengage the voltage meter and close the hood.

Tips and Warnings

  • In many cases, what seems like a bad alternator or battery is really just a loose wire. Always check wiring to make sure that all connections are nice and secure. If your battery terminals are corroded, you should clean them. Corrosion can interfere with the electrical function of your car.
  • If your alternator needs to be replaced, you will probably notice some small problems with the electrical components of your car. Dim headlights are often the first sign followed by a slow, sluggish start. The battery will continue to be drained of power until, eventually, the car will not start at all. All of these signs may indicate that you need a new battery as well, so it is very important to check the alternator before you make unnecessary purchases. Fortunately, it is very easy to check the alternator on your car.