2001 Cadillac Deville Battery Drain

  • 1 POST
  • V8
  • FWD
  • 75,000 MILES

Started with Airbag Light coming on and Radio fading. Installed new battery. Airbag Light is off now. Radio does not function. Clock on radio blinks slowly. Battery drains overnight.

Mechanic removed radio every fuse one at a time to see if drain continued and it did. Now mechanic is looking to disconnect BCM? VCM? To see if drain continues.

Any thoughts?

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Tuesday, September 15th, 2015 AT 1:31 PM

1 Reply

  • 29,781 POSTS

I suspect you're in the wrong area. If the Air Bag light turned on while driving, the electrical system would have been running on the generator and a drain would be irrelevant.

Also, for a drain that runs the battery down while the car is sitting overnight, pulling fuses is not the way to start the diagnosis. There are computers on the car that go to "sleep" mode after as much as 20 minutes after stopping the engine, and until that happens, there can be a huge drain on the battery, ... As much as three amps. Doing anything that breaks the circuit to one of those computers wakes it up, then the high current draw starts all over until it goes to sleep mode again. Breaking the circuit is done by removing a battery cable to insert an amp meter, by pulling fuses to that computer, and even by switching scales on the amp meter. There is an entirely new procedure for testing for a drain, but it sounds like you have a generator problem.

The place to start is by measuring the battery's voltage with the engine stopped, then with it running. With the engine off, its voltage should be 12.6 volts. If it's around 12.2 volts, it's good but discharged. It needs to be charged at a slow rate for an hour. If it's okay, the next measurement is taken with the engine running. Then the voltage must be between 13.75 and 14.75 volts. If it is low, suspect the generator. GM has had a lot of trouble with their current generator design. To reduce the number of repeat failures, replace the battery at the same time, (which you already did), unless it is less than about two years old. As they age and the lead flakes off the plates, they lose their ability to dampen and absorb the harmful voltage spikes these generators develop.

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Tuesday, September 15th, 2015 AT 4:48 PM

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