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Voltage drops

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2002 - 2009 GMC Envoy
kerux12345

I'm having a problem with the voltage dropping suddenly while driving at highway speed. It never seems to do it while driving at lower speeds. The headlights dim a little and I look at the voltage meter and it drops to 12 volts (from the 14volt norm). It goes back up usually in 3 to 5 seconds. The alternator and battery tested ok.

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Response from good2us

1:15 am December 17, 2016

I don't have this vehicle, but our 2007 Chevy Uplander occasionally (once or twice every few months)does this. Normally, our voltage output cycles between 13.4 and 15.2 volts. It has never had any other electrical issue (or symptom of one), but I'm posting because your Envoy may have current sensors around the power cable from the alternatorlike ours (which are used to adjust alternator output) and perhaps that could be a cause of what you're experiencing. BTW, we have about 183000 miles on our van. I hope this either helps you get to the bottom of the problem or gives you peace of mind (if your symptoms are as infrequent as ours).

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Response from kerux12345

12:10 pm October 10, 2017

Just a follow up on this problem. It was a bad alternator. It tested fine in the vehicle but once I took it out and had it bench tested, it clearly failed. I put a new alternator in and it is is working fine.

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