After the faulty alternator was replaced, the battery caption remains on, but everything is OK

 

Ooh, this one is easy. Was an aftermarket replacement installed? The regulator inside the OEM version has a special extra circuit for the battery light. Aftermarket versions, even if charging properly, don't have this capability.

The light isn't controlled directly by the alternator, unlike most vehicles. Instead, special OEM circuitry in the alternator's internal regulator will monitor the charging output and send a valid signal if all is good. The receiving computer (sorry, don't know its name offhand) turns on the warning light any time the valid signal is not present.

I think it's possible to swap the regulator from the failed OEM alternator into the aftermarket unit. As long as the original regulator is still good, that should take care of the missing valid signal.

 

Oh I have heard some/all after market replacement alternators will not put out the charge light . Somthing to do with non compatable ic reg .
The thing to do here is not to throw out the old alty and get it overhauled . Then swap them back ,

 

I....didn't....know....that! Thanks you two guys.

 

This morning I awoke to the battery light being on in my car. Have a 6 month high end AGM battery but tested anyway with car running and was at about 12.03 volts and amps were in negative. Knew it was the alternator and more specifically the regulator. Went and was able to get one at O'Reilly. Did not know if the l signal would get sent or not, but after installation, everything worked fine and no battery light and it was a re-manufactered one. Of course, I could have been lucky on the parts inside that were redone. However much cheaper than giving money to the arrogant thieves at the Jag Dealership. Here is a link and it works fine.

Ultima 11199 - Alternator | O'Reilly Auto Parts


Tom in Dallas/Plano
2005 S-Type 3.0 91k