Voltage regulation

DAKOTA5

MEMBER
2003 CHEVROLET CAVALIER
4 CYL
AUTOMATIC

I have a 2003 chevy cavalier that seems to have a voltage regulator problem. With my multimeter hooked up off an extension wire (positive to the positive battery terminal and negative to the frame) I am getting the following readings. Idle- 13.8 volts, driving with no extra electrical on - 12.6 volts, driving with lights on - 11.8, then turn on heater blower on - 11.2 volts. When I brake, then voltage will spike even lower. When it gets to this low voltage the SES light and theft system lights come on and the gauges quit working. Turning off anything using electrical makes the gauges work again but the service lights do not reset unti the engine is turned off and restarted. I replaced the alternator with one from the salvage yard and the voltage readings were good (14.6) for about 5 minutes and then the car reverted to the erratic readings. Any ideas?

1 Reply

CARADIODOC

MECHANIC
33,738 POSTS

Buy a rebuilt generator, not a used one. This is the worst pile GM ever produced and they have no intention on improving it. It is common to go through four to six of them in the life of the car. What many professionals are finding out is to reduce the number of repeat failures you must also replace the perfectly good battery at the same time. It will work fine in a pre-1987 car but as they age they lose their ability to dampen and absorb the huge voltage spikes this generator design produces. Those spikes damage the internal voltage regulator and diodes, and can interfere with the various sensor signals resulting in running problems.

Dandy testing techniques, by the way. Your voltage readings and diagnosis are right on.