I just noticed on my 2000 sunfire gt 5 speed (87000 kms) that the odometer and factory stereo displays lights were flickering with varying brightness levels. I tested the voltage at the battery with the car idling and it jumps around from 13.0 - 15.5 volts. The car runs normal still and starts normal but there is obviously a voltage problem.

Do these cars have voltage regulators built into the alternators or do the PCM's control alternator output? I just replaced the original alternator two months ago and a new battery was installed 12 months ago.

I doubt there is a wire or connection problem since the voltage is running high rather than too low. The connections all look good with no corrosion or rust.

Does anybody have an experience with such a situation?

Yes the voltage regulator is in the alternator like with most (I think all) newer cars. It sounds like your voltage regulator is going out, you have a bad battery cable, or alternator wire (batt wire), or your battery is just too old and isn't wanting to charge correctly.

Sounds like the alt is screwing up. i have had Advance auto parts alternators do exactly what your describing.
The reg is in the alt, and the pcm enables the charging. pcm doesnt tell the alt how much to charge just whether to or not.


01 cav w/01 3400 gam gt 4t45e

pb blast all your grounds.. battery and engine block before you go spend a lot of money... make sure your terminals are clean and snug...

"Z24 Dustbunny"

If you've been jump-starting people with your car running.... you've likely killed the voltage regulator in the alternator. Needs a new board....