My dang car.

MATLOCKB

MEMBER
HONDA

I got the charging system light on my dash. Mistakenly diagnosed as alternator by pulling the negative lead (apparently that doesn't work anymore.) So I pulled the alternator. It tested good at two auto parts stores, but the battery tested bad. I checked all my ground cables, fuses, and could find nothing else wrong. Put it all back together with a new battery, and the light cleared. Started it and drove to work this morning, and after about 15 minutes (as soon as I got into fifth gear getting on the highway) the light came back and stayed.) Any ideas?

1 Reply

BRUCE HUNT

MECHANIC
3,754 POSTS

Here are my three cents worth (inflation) on alternators. Checking them is not an ironclad deal that they are working correctly. The battery tested bad and you replaced it. Did you happen to notice why it was bad? The alternator can fail in a number of ways. 1. The bearings can go out and take it out of action. Pretty easy to diagnose. 2. The system fails to charge at all for numerous reasons. Again pretty easy to find with a volt meter. 3. The system charges just fine but doesn't know when to shut off. That one is tough to diagnose, but the battery will have a number of possible problems. The battery can be dry of water, bad cell, etc.

Long story short, don't positively accept that the alternator is good.