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Q: ALTERNATOR ISSUE?

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I HAD AN ISSUE WITH MY CHECK ENGINE LIGHT TURNING ON. I TOOK IT TO A LOCAL MECHANIC AND HE DID A BUNCH OF CHECKS. WHEN TESTING THE ALTERNATOR HE NOTICED THAT WHEN HE STARTED THE ENGINE THE VOLTAGE JUMPED FROM 12.5V TO 14.5V LIKE NORMAL. THEN ALL OF A SUDDEN THE VOLTAGE DROPPED BACK DOWN TO 12.1V AND NEVER CAME BACK UP WHILE BEING TESTED. IS THIS ISSUE IN FACT A ALTERNATOR ISSUE? I CAN'T SEEM TO FIND ANY INFORMATION ABOUT THIS ISSUE.

My car has 157000 miles.
My car has an automatic transmission.

The voltage put out by the alternator is typically in the range of 14.2 V to 14.5 V as measured right across the battery posts. If the charging voltage is outside that range, then there is a problem with the charging circuit. The charging circuit includes the wiring, alternator, voltage regulator (often integral with the alternator), fuse link, and all terminal connections. So long as no fault is found in the wiring, fuse link and terminal connections, as measured using standard voltage drop testing, then typically the alternator would be condemned and replaced. Preferred replacement sources for the alternator are dealer OEM new, re-built dealer OEM, and aftermarket reputable name brand vendors such as AC Delco, Bosch, and so forth which may carry both new and rebuilt lines. New alternators are of course the preferred choice. If you desire that the charging system on the car be diagnosed for confirmation that you need a new alternator the recommended service is a charging diagnostic. Please let us know if you have additional questions.

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