Volt light keeps coming on

Tiny
MZSMITH
  • MEMBER
  • 1995 BUICK LESABRE
  • 57,000 MILES
I have a 1995 Buick LeSabre. It has been to the dealer 3 times for the same problem - the battery light keeps coming on. The alternator has been replaced with a new one. The second and third time - the mechanic went thru the car: cleaned battery terminals, replaced alternator L Pin connector, repair 1 remanufactured generator core charge C, core return. When the battery light is on, the battery is not charging. Every time I leave the dealership, the battery light does not come on for approximately 2 weeks. Then it comes on more and more often and stays on for longer periods of time. I am frustrated beyond belief with this - what is the problem? When the light is on, the battery is not charging - this has been verified.
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Sunday, April 28th, 2013 AT 2:55 PM

6 Replies

Tiny
CARADIODOC
  • EXPERT
Hello,

There's two ways the alternator can stop working intermittently. If the battery light turns on and the alternator stops charging after the engine has been running a while, that is due to an intermittent problem inside the alternator, typically the voltage regulator, or a bad connection in the larger wire going from the back of the alternator to the battery. A bad connection will stop the alternator from charging but it may not turn the light on.

The other potential cause is a break in the wire between the battery light on the dash and the smaller wire plugged into the back of the alternator. Besides being the warning light circuit, that is the "turn-on" signal from the ignition switch that it's time for the voltage regulator to turn on and start running the alternator. Once the engine has started running and the alternator is turned on, that circuit can be thrown away and the system will continue to work until the engine stops running. An intermittent connection in that circuit will only cause the charging system to not start up and work. It will not cause a problem after it has started working. Also, if the "battery" light turns on, that proves that entire part of that circuit is working, so for all practical purposes that leaves the generator as the only logical suspect.

Also what happens on these cars is the PCM goes out and it cant control the alternator output so it shuts it down. Here is an alternator wiring diagrams o you can see how the system woks.

Here is the PCM location I would get a used one and plug it in to see what happens.

Check out the diagrams (Below)

Please let us know what you find.

Cheers
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Sunday, April 28th, 2013 AT 3:04 PM
Tiny
MZSMITH
  • MEMBER
Should the diodes int he alternator also be replaced also?
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Sunday, April 28th, 2013 AT 3:16 PM
Tiny
CARADIODOC
  • EXPERT
Nope. The six diodes are a part of the alternator
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Sunday, April 28th, 2013 AT 3:27 PM
Tiny
MZSMITH
  • MEMBER
Thank you for your time! So, I should see about replacing the PCM. My battery is older than 2 years. However, even with an old battery, when the engine light goes off, the battery recharges... This is what has been keeping me away from purchasing a new battery - particularly troubling for the 2 mechanics who are troubled by this as well. My mechanic close to home would love to know it could simply be a battery problem - as would I have. Then I went for it I got a used PCM and BAM fixed it. This site is smarter than the dealership wait until I tell them I fixed the problem going to blow their minds. Thanks again.
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Sunday, April 28th, 2013 AT 3:44 PM
Tiny
CARADIODOC
  • EXPERT
Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help

Cheers
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Sunday, April 28th, 2013 AT 4:32 PM
Tiny
MZSMITH
  • MEMBER
Thank you so much for your time - you have been most helpful!
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Sunday, April 28th, 2013 AT 5:13 PM

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