How to Check the Alternator Output on a GM

The alternator is a device under the hood of your car that is spun via the serpentine belt. While the alternator is spinning, it is charging the vehicle's battery, so all the electrical components of your car work properly. It is a small, cylindrical device in the top left corner of your engine. Alternators eventually need to be replaced. When they quit working, they won't charge the battery and your car will not start. Before you buy a new alternator, you should test the current one with a volt meter to make sure it is broken.

Things You'll Need

• Volt meter

Instructions

1. Start your GM vehicle.

2. Turn your volt meter on. Switch it to the DC setting.

3. Place the red lead from the volt meter to the positive red terminal of the GM battery.

4. Place the black lead from the volt meter to the negative black terminal of the GM battery.

5. Read the volt meter screen. It should be between 13.5 and 14.4 volts. A battery only has 12 volts, but while the car is running, the alternator spikes the volts to 14 to overcome resistance.

Tips & Warnings

• If your GM vehicle doesn't register between 13.5 and 14.4 on the volt meter, then you need to replace the alternator.

References

• Test Alternator