Battery Warning Light

Tiny
PSBRANDON
  • MEMBER
  • 2002 PONTIAC GRAND AM
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 277,000 MILES
Driving on the highway, wet roads, my battery warning light came on. The headlights dimmed and the blower fan slowed. Soon after, the ABS light, then the emergency brake light, then the tract light. Then the gauges zeroed and stopped working along with all the lights. The car was stuttering (assuming I was driving on the alternator output alone). I took the battery out and it tested as bad so I replaced it. I was still seeing the battery warning light so I tested the output of the alternator at warm idle. The output was between 14.5 volts and 15 volts. Now, after driving it home, I am noticing the battery warning light comes on, then goes out repeatedly. I am thinking a loose connection somewhere but I do not know where to look. I should also mention that yesterday I replaced a rear brake wheel cylinder. I am not sure if the wheel sensor on the side I replaced the wheel cylinder could be linked to this problem.
Monday, February 6th, 2017 AT 11:35 AM

4 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
You were not driving on the generator when the problem occurred. You were driving on the battery, and that is only going to last about a half hour. The multiple warning lights were due to the various computers shutting down from low system voltage.

What has most likely happened is the generator failed due to the bad battery. GM has had a real big problem with that since they redesigned their generators for the 1987 model year. GM generators develop huge voltage spikes that can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. The battery is the key component in damping and absorbing those harmful spikes, but as it ages and the lead flakes off the plates, it loses its ability to do that. To reduce the high number of repeat generator failures, the battery must be replaced at the same time, unless it is less than about two years old.

Since you have the new battery already, the most likely solution is to just replace the generator. It is not practical to try to repair it. This one was not designed to be taken apart.
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Monday, February 6th, 2017 AT 1:54 PM
Tiny
PSBRANDON
  • MEMBER
  • 8 POSTS
I replaced the alternator today and the light is still on. Could it be a short at the wheel sensor I was working around a few days earlier?
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Tuesday, February 7th, 2017 AT 1:07 PM
Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
No. You are looking at two totally different systems.

The next thing is to determine why the warning light is turning on. Connect your voltmeter to the large output stud on the back of the generator in such a way that you can see what the charging voltage goes to while you are driving and the "battery" light turns on. If the voltage drops to less than 13 volts, the generator is quitting. If it goes real high, as in 16 volts or more, suspect a break in the fat wire going back to the battery.

How many wires are there in the small connector at the side/rear of the generator? There will be a brown wire. Are there any others?
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Tuesday, February 7th, 2017 AT 2:36 PM
Tiny
PSBRANDON
  • MEMBER
  • 8 POSTS
There are two wires (see diagram). I will try what you suggested.
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Tuesday, February 7th, 2017 AT 3:16 PM

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