Electrical experts out there?

[BBHOE]

I have a 2007 Tahoe LT3, I've been having a hell of a time diagnosing this weird electrical issue, intermittently I will get a fault code for ignition voltage below 9V fault code P1682, no rhyme or reason to it sometimes it will come back once a week or every other day, battery and charging systems are both OK, only weird thing I noticed was at times my charging gauge will go to 16V, 14V, and 12V. I have a scan tool but it only reads faults and basic PID's.

Any suggestions?
Thanks

 

[OklabyGodhoma]

The voltage varies is normal. If I may suggest that you first do a couple of basic things just to have a good starting point. If you have a meter take a voltage reading directly at the battery terminals with the engine off and again with it running. Next check terminals for ANY signs of corrosion and also verify tightness with a wrench on the terminals. Next start wrench testing other positive connections. A common fault has been a loose connection on the buss bar located on the firewall just behind and to the right of the battery.

Have you ever replaced the battery? How old is the current battery? What brand? What size as to the cold cranking amps?

Once I have that info we can continue. My guess is that you may find a bad connection.

 

[BabyHuey]

I would recommend also gettign you alternator checked at like autozone or whatever to make sure its charging correctly also. They shoudl do it for free....may point to the problem

 

[mike1944]

Plus one for cleaning and tightening the battery cable connections first. Computer doesn't like erratic voltage - makes it crazy.

 

[BBHOE]

Thanks for the replies...
First off, battery is fairly new (about 6 months old) AC Delco battery 700 CCA, with the key off the battery reads 12.4 V, with engine running its about 14.1 V. Performed a load test and battery, battery and charging system OK. No signs of corrosion, I removed both cables and cleaned them anyways with wire brush...

After a few hours of messing around I noticed that when I shut off the key, the CEL stays illuminated (very dim) for about 30 seconds, then shuts off. After that each time I turn the key on it sets the fault. Now knowing that, I have come to a few lead points, I recently installed a sub and amp to the factory radio, I used an adapter and splice into the speaker wires at the amp for the RCA's, and the remote wire is spliced into a power wire at the BCM. If I unplug that wire the fault does not come back, which leads me to my next question?

Is there anywhere to installed a remote power wire that comes on and off with the key that won't interfere with the vehicle entering its 'sleep mode'.
Sorry I don't know the technical terms, I'm a BMW tech and thats what we refer to it on those cars.

Thanks

 

[OklabyGodhoma]

You should be able to pick up a B+ source in the BCM located just above your left foot under the dash.