Battery Light

  • 94,010 MILES
My battery light came on but my vehicle runs fine. I unplug the battery while running and it does not die and it starts right up when the battery plugged in. What could this problem be? Also, is there a chance the car can die when driving now? I have to be somewhere in the morning and wondering if there is a chance of it quitting?

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Tuesday, October 18th, 2011 AT 3:25 AM

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I would scream at you for disconnecting the battery while the engine is running. That was a test done many years ago by mechanics who didn't understand how these simple systems work. What saved you is you have the world's second best generator, and your car doesn't have many computers that will be damaged from high system voltage. The battery is the key component in helping the voltage regulator keep the system voltage safe and steady.

Beginning with the '87 models, GM went to the worst design ever in generators. Disconnecting the battery will often cause numerous computers to be damaged.

The proper test is to use an inexpensive digital voltmeter to measure battery voltage while the engine is running. It must be between 13.75 and 14.75 volts. If you look closely at your battery light, I suspect you're going to find it is not on real bright. That's what happens when the generator has a defective diode trio. That part routes a little current back to run the field winding and it turns off the battery light. When one of the three diodes is open, output current is reduced and the light is not turned off completely.

The voltage regulator also sees the momentary drop in output and responds by raising output voltage. You will likely measure a fuzz higher than 14.75 volts. If that sounds like what's happening, I can walk you through the steps to replace the diode trio.
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Tuesday, October 18th, 2011 AT 3:37 AM

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