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 MuscoplatPosted on by Rick Muscoplat