2002 Pontiac Grand Prix Battery issues

  • 3.8L
  • V6
  • FWD
  • 167,167 MILES
I recently had to replace my battery after about 5 years. I figured with all the cold weather we have been having and the age of the battery that it was just a simple issue. After installing the new battery, approx. 24 hours later I went to start my car and it was difficult to start, but when it finally did the battery light was on on the dash. After about 15 minutes or so it finally went off. The next couple of days it did the same thing. I had autozone test my battery and alternator and they said it was fine. My dad knows a bit about cars and did his own test, (take the negative cable off, the test you have mentioned on here), and said that it was not the alternator draining it back. We went through the car piece by piece to figure out what the problem was and it came out being the "stereo amp" (I did not even know there was an amp in there, but turns out there is a factory installed BOSE system). So I pulled the fuse on it and so far that has solved the battery dying problem. On the other hand, now my radio does not work. I am trying to figure out if the amp can be bypassed from the rest of the stereo until I can either replace it or get it repaired, without damaging anything, OR if this is something easier and more simple to fix, such as a fuse. The fuse that I took out was not broken internally but it was rather charred on the prongs. And also, previous to this happening, for most of last summer while driving and occasionally hitting a hole in the road, something would start whining and sounded like it was coming from the speakers. Everyone I talked to about that said it was a ground of some kind. As you can probably tell, I do not know a whole lot about cars, but am trying to learn. Although my dad knows more than I, he does not know how to fix this problem. I am really hoping you can help. Thank you.
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have the same problem?
Tuesday, February 18th, 2014 AT 6:54 PM

1 Reply

I'm confused about your comment about removing the battery cable. Did you do that with the engine running?

Second, only all Chrysler radios put out speaker-level output and any radio will work in any car with or without a factory amp. On GMs and Fords, some of their systems use remote amps and some don't. Those radios that do, you must use the amp or you won't be able to hear anything. Those radios that don't use an amp can't be used with one because the sound will be too loud and garbled.

The third thing to be aware of is GM has had a huge problem with their generators since they redesigned them for the '87 model year, and they have no intention on improving them. They make too much money with this problem. Due to their design, they develop large voltage spikes that can damage the internal diodes, voltage regulator, and interfere with computer sensor signals. It is common to go through four to six replacement generators in the life of the vehicle. To reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old. As they age, they lose their ability to dampen and absorb those voltage spikes.

It is not common for a battery to not cause a problem in five years in a GM product. I would want to see the test results on the generator before I agreed it was okay. Auto parts stores rarely have professional load testers. Usually all they do is measure the battery voltage while the engine is running. That must be between 13.75 and 14.75 volts, but that's just the preliminary test. They also commonly have bench-testers for generators but those also don't tell the whole story. All generators are very inefficient at low speeds. That's why for accurate testing, it must be done with it on the engine, and engine speed is around 2000 rpm. That takes around five to eight horsepower to run the generator wide open. Bench testers usually have 3/4 or 1 horsepower motors, so they can't possibly run the generator wide open or fast enough. All those testers will tell you is if you have something, not how much.

The second part of the test involves that load tester I mentioned. It will draw the maximum current the generator is capable of, for a few seconds. When one of the six diodes has failed, you will lose exactly two thirds of the generator's design capacity. 30 amps from the common 90 amp generator is not enough to run the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over hours or days. "Ripple" voltage will also be very high. That is measured by professional load tester, but not by the smaller hand-held portable testers.

On GM vehicles, the voltage regulator runs the dash warning light, and it will not turn it on for a failed diode or a low-charge condition. Since your light IS turning on, that suggests something else is wrong, and the most likely cause is worn brushes. They can make intermittent contact, and may start to work for a few months when the engine warms up and parts expand. Measuring the battery voltage will identify that, but any testing has to be done while the problem is occurring. Brushes are easy to test on all Chrysler alternators and on '90s Ford generators, but they are buried and inaccessible on GM generators. They are easy to replace too on all Chrysler products, but the engineers at GM designed theirs to be extremely frustrating to get apart. The first ones were even riveted together so people couldn't try to fix them. The aftermarket tool manufacturers had to come up with ways to get them apart. Even now, with generators that are bolted together, it is still a frustrating ordeal to take them apart. You are almost guaranteed to break off the flimsy tin tabs on the diode block, so that will be junk, and once it's apart, there's no way to test the voltage regulator or the brushes. You'll have to replace all those parts to insure you found the cause of the problem. THEN, they also have lots of bearing trouble so you'll want to replace those too. To get such high current out of a little package, the clearance between the stator winding and the rotor is extremely tight, so a little play in one of the bearings will cause the generator to lock up and stall the engine.

Given all those problems, all my students can do is take them apart to see how they're built. To put together a working generator we have to use any other brand. You can buy rebuilding kits for all generators, but by the time you're done with the diode block, voltage regulator, brush assembly, and bearings, for just a few dollars more you can get a professionally-rebuilt generator with a warranty.
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Tuesday, February 18th, 2014 AT 7:55 PM

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