Rick's Free Auto Repair Advice

Testing alternator by removing battery cable

Can you test an alternator by removing battery cable?

Technically yes, but that test can also wind up destroying all the electronics in your car; PCM, TCM, electronic power steering, radio, etc. Testing alternator by removing battery cable was a valid test back in the day before computers. But it’s no longer a safe test to perform on a modern vehicle.

The instant you disconnect the battery cables to test the alternator, the alternator goes into “full field” mode where it can generate a voltage spike as high as 150 volts! Yes, you read that correctly. That’s because the battery acts as a capacitor/shock absorber in the system. Without it, full alternator output voltage can spike to 150-volts, more than enough to fry every computer in your vehicle, along with your stereo, fuses, remote door locks, etc. Reconnecting battery cables generates a second spike.

Never test an alternator by removing battery cable

At least not on a modern vehicle with computers. Instead follow the testing procedures in this post

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat



Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN