2002 Montana voltage regulator keeps shorting out

Tiny
RRMBAJ
  • MEMBER
  • 2002 PONTIAC MONTANA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 180,000 MILES
I have a 2002 Montana and have put in my third alternator within 4 months. Battery is good, voltage is 12.51 and holding a good charge. I originally replaced the alternator after the battery light came on and eventually lost all power. Out of the last two alternators installed, one lasted 2 months and the other 2 weeks before shorting out the voltage regulator. I began inspecting the battery cables and leads to the alternator for a short but am not really sure where to focus. Any suggestions would be appreciated.
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Sunday, May 8th, 2011 AT 9:14 PM

5 Replies

Tiny
DOCFIXIT
  • EXPERT
Are you checking PCM for codes? Using BOSH new or rebuilt? Was ALT output checked after install?
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Sunday, May 8th, 2011 AT 9:23 PM
Tiny
CARADIODOC
  • EXPERT
Replace the battery. This is by far the worst pile ever as far as generator designs. By its very nature it develops huge voltage spikes that interfere with sensor signals and can destroy the diodes and voltage regulator inside the unit. It is very common to go through four to six of them in the life of the vehicle, although not as fast as you are, but what many professionals are finding out is to reduce the number of repeat failures you must replace the perfectly good battery at the same time. As they age, they lose their ability to absorb and dampen those voltage spikes. The old battery will work fine in a pre-1987 vehicle.
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Sunday, May 8th, 2011 AT 9:41 PM
Tiny
RRMBAJ
  • MEMBER
No faults detected, checked frozen data as well. The alternator came from Auto Value, 120A and don't recall the brand. I did not check the output after install. Thanks for the reply.
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Sunday, May 8th, 2011 AT 9:47 PM
Tiny
RRMBAJ
  • MEMBER
The battery is 5 years old, it may not be a bad idea to change it out. When I checked voltage all seemed fine but to your point there may be voltage spikes I am not aware of. I was not aware how sensitive the alt is on this van. Good suggestion, Thanks.
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Sunday, May 8th, 2011 AT 9:53 PM
Tiny
CARADIODOC
  • EXPERT
Shirley. I mean "surely"! Appears I interrupted your conversation with Docfixit. Sorry about that.

This is a real common problem with a real common fix.
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Sunday, May 8th, 2011 AT 9:58 PM

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