Low voltage caused by PCM

NewfieEnvoy

Original poster
Member
Jan 25, 2012
525
So I've been finding a few threads on this subject but no definitive answers, but I know I'm not the only one who experiences this.

One cold start I'll read around 14.7 volts, but after warming up and hitting the road the voltage will sometimes drop to around 12.5. After a little while it may come back up on it own or I can force it up by placing more load on the alternator, rear defog-headlights-fog lights-etc. On the OS I see Roadie posted that the PCM maybe doing diagnostic testing to check the battery condition. Do we know this for sure? Has anyone found anymore information regarding this brilliant GM phenomenon :hissyfit:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
That specific phenomenon I was discussing was a SAIS diagnostic, run by the PCM, to diagnose the SAIS. But the PCM might run diagnostics at any time that could involve turning off the alternator. Adding load to the alternator should REDUCE voltage, not increase it.

Pull the fuse (front #56) for the SAIS turbine pump for a couple of days and see if it changes its behavior.
 

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