1997 Jeep Laredo spike in voltage on gauge

JIM R JOHNSON

MEMBER
1997 JEEP GRAND CHEROKEE LAREDO
6 CYL
4WD
AUTOMATIC
145,000 MILES

My battery died two weeks ago, replaced and yesterday the lights on dash were flickering. Today the voltage gauge spiked all the way to the right (+) and held for 30 sec, went off and did this a few times within a half hour. Went to Shucks and they did a check on the alternator and said it was o.K, the battery was down though. There was no spike present at the time of the test. Any ideas? Thanks!

Friday, November 14th, 2008 AT 6:44 PM

1 Reply

JAMES W.

MECHANIC
2,394 POSTS

There are diodes in the alternator that convert 3 phase voltage into DC voltage. If one or two of these diodes goes bad or comes loose, the voltage can spike to over 100 volts. When it comes to auto computers and other electronics, this is a "bad" deal. I wouldn't start it again until I changed the alternator. Just to give you an idea, there is an alternator kit you can buy for some vehicles that bypass's these diodes and run an ordinary electric drill off the output. Yours is the first case I've heard of in years, but it does happen. Hope this helps and thank you for the donation, Jim

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Friday, November 14th, 2008 AT 7:10 PM