Thread: 2004 Grand Prix

My son bought a 2004 Grand Prix and about a week after buying it it wouldn't start and he got a "charging system failure" message. The dealer we bought it from tested the battery and said it was bad so he replaced the battery. A couple of weeks after putting in a new battery we got the same message. We had the alternator checked and was told it was good. What else could be the problem. Does the cars computer system need to be reset.

I have a 04 comp g and second gear has decided to choose when it wants to engage. So I'm interested in what others transmissions can I swap with.

If your son's model comes with the screen in the dash where you can see the battery voltage while driving, then that's a great diagnostic tool because it gives you the voltage the alternator is supplying continuously to diagnose if the alternator is acting up. If it's not, then get a $10 OBDII bluetooth gizmo from ebay and download an app like "torque" on a phone/tablet or a laptop and use to monitor the voltage. Best is a smart phone so he may attach it in front of him while driving with the app on and a battery voltage gauge is always on.

If the grounds and fuses/relays are good, and the voltage sometimes goes too far outside the 13.5-15V range when the engine running, or if the voltage has a high AC component (use a meter on AC volts) then it should be a bad alternator.

Through the years, I learned that most of the times, the only mechanical part in an original alternator that fails is the bearing and the only electrical part is the diode(s) at the back of the alternator (they usually either look like big black cylindrical diodes just like the ones you see in power supplies and electronic boards or small cubes soldered to a washer-like board). I recommend repairing an original GM alternator, rather than replacing whenever possible.