1999 Cadillac STS



November, 25, 2007 AT 10:42 AM

I got a 99 cadillac sts with 160,000 miles and the 4.6 northstar motor. The problem I've been haveing is with the charging system of the car. After purchaseing the car I found out the alternator was bad and recently replaced that but when I replaced it still did not charge the cars battery but did provide the power after start up to run the car. Monitoring the voltage I notice it would operate at between 12-16 volts depending on the RPM of the engine whiched seemed to be unusually low/high. Usually this car would run about 13.5 volts with minor fluctuation. Also because of the high voltage it would trip warning lights including the abs, traction control, service engine soon, security, and also cut out the rear audio amplifier. This problem also caused the alternator to burn itself out in a matter of a few days probably due to the high voltage output. This would be the third alternator within one year. I believe the warning lights have only appeared because of the voltage/charging problem. I believe this because I disconnected the alternator from the car itself under the hoods fuseblock and reset the cars computers. I ran the car all day only running off the cars battery (with alternator disconnected) and not one warning light or problem besides the battery indicator. I also replaced the PCM and DIM computers thinking this may have been the problem but did not solve it. Any help would be much appreciated.


3 Answers



November, 26, 2007 AT 4:22 AM

The computer controls the field generation of the alternator. Make sure the alty. Is properly grounded-to include the computer-you probably have to check wire to wire from the alternator to the igniton switch and computer.



November, 30, 2007 AT 10:39 AM

Where have you been buying the parts at? Autozone?



May, 18, 2008 AT 9:40 PM

Yes I did get the alternator from auto zone but when I got the car the prevoius owner was haveing the same problem and he got a delco one and had them install it at a dealership. I recently got my hands on a perfectly running donor car from a friend that let me swap some computers out to diagnose my problem. Still the problem persists. All fuses and relays seem to be good. I got my hands on a wire diagram to try to figure this out. Any help would be greatly apprieciated

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