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Spent a whole Saturday chasing a 'bad' alternator that was just a loose ground | Auto Mechanics - Librear

Spent a whole Saturday chasing a 'bad' alternator that was just a loose ground

I had this 2012 Civic come in with a classic no-charge light. My meter showed 11.8 volts at the battery, so I figured the alternator was cooked. I pulled it, sent it to the parts store for a bench test, and they said it failed. I put the new one in, fired it up, and still had 11.8 volts! I was so confused. I spent the next three hours checking every connection and fuse, getting ready to blame a bad PCM. Finally, I jiggled the main engine ground strap near the firewall and my meter jumped to 14.2. The bolt was just a quarter-turn loose. I wasted $140 on a core charge I couldn't get back and a full day of my weekend. Always check the simple stuff twice, even when the test says otherwise. Anyone have a good method for a quick ground check before pulling major parts?

3 comments

3 Comments

lane.kim7mo ago

My old boss at the tire shop had a saying, "Chase the volts, not the parts." He meant to follow the voltage drop with your meter from the battery out. I keep a set of jumper cables in my toolbox just to make a temporary ground from the battery to the engine block. If the voltage jumps up, you found your problem in about thirty seconds. It's saved me from pulling a starter more than once. That sinking feeling when the new part doesn't fix it is the worst.

faith127mo ago

Yeah that's a solid method from @lane.kim. People forget the ground side is half the circuit. I've seen guys spend an hour on a no-crank only to find the ground strap from the engine to the frame was just hanging there, looking fine but not making contact. Your jumper cable trick proves it fast. Saved my butt on an old truck where the battery cable itself was corroded under the insulation, showed 12 volts at the starter but it couldn't carry the load.

calebscott6mo ago

Remember to check the ground connection on the starter itself too. Had a car where the mounting bolts were painted and the starter wasn't grounding through the block properly. A quick scrape of paint and it cranked right over.