Intermittent Electrical Issues

[AzDragonLord]

2009 Sierra WT with towing package...56k miles

 

I've been noticing a slight flicker from all my lights (headlight, dash, etc) when a load was placed on them...like when using a turn signal, brake, etc. At first I thought it was my imagination, but this morning it got a lot worse! At highways speeds my headlights would momentarily go completely out, and it was more pronounced with increased engine RPMs. This morning it even caused a momentary ABS alarm while driving. While idling in a parking lot I can see a barely visible flicker from all my exterior lights. Onstar diagnostics didn't show any issues.

 

I'm thinking it might be the alternator or regulator, but I'm not sure. Any other thoughts on this problem? I commute over 100 miles per day in mountain terrain and would like to get this issue resolved quickly.

 

Thanx in advance!

[Wolfmanjohn]

Check grounds first. Then, if necessary, start checking for power supply/delivery issues.

[kstruckcountry]

Is your alternator at ~14?

[AzDragonLord]

It's intermittent, so it might be tough to catch it in the act though. If it's going to fail...I wish it would fail completely.

[00Silverado4x4]

Be careful what you wish for...

[AzDragonLord]

Since most things in these trucks are connected to a control module of some sort, I wonder if that might play a part in this?

[AzDragonLord]

I purchased a Bluetooth OBD2 Diagnostic Scanner, and using the "Torque" app on my phone I was able to watch the voltage fluctuate between 14.3v all the way down to 12v....all with the engine running. I would have expected a warning light if the alternator was failing, but I had no warning lights.

[AzDragonLord]

_{Yesterday my truck acted up again, but this time it was completely different. The radio cut out, engine lost power, air bag and CEL warning lights came on and the gear selection indicator went bonkers. I had just turned into traffic when this problem occured, lasted about 10 seconds, then went away. I didn't notice any message on the DIC, but with everything happening at once I may have missed it. I checked my Torque App for codes and found none. I don't see any common ground between this and the first incident either...bumps, rain, temperature, etc.}

 

_{Seems to be totally random which worries me. I work on computers for a living, and this smells like an intermittent computer malfunction to me. One of the control modules must be faulty or have a loose/damaged harness...but which one and where is it located?}

[robertdegoey]

_{Yesterday my truck acted up again, but this time it was completely different. The radio cut out, engine lost power, air bag and CEL warning lights came on and the gear selection indicator went bonkers. I had just turned into traffic when this problem occured, lasted about 10 seconds, then went away. I didn't notice any message on the DIC, but with everything happening at once I may have missed it. I checked my Torque App for codes and found none. I don't see any common ground between this and the first incident either...bumps, rain, temperature, etc.}

 

_{Seems to be totally random which worries me. I work on computers for a living, and this smells like an intermittent computer malfunction to me. One of the control modules must be faulty or have a loose/damaged harness...but which one and where is it located?}

 

 

I wonder if the aftermarket cruise you have has damaged your PCM. I've read about some aftermarket cruise control's causing damage to them. Not sure if it was Rostra or not. Sounds like more than a ground or alternator issue though, especially after the last incident.

[gmtech4]

dont throw parts at it ,have your battery checked and alternator checked

[AzDragonLord]

That's the problem with intermittent failures...they never present themselves when it's convienient!

 

The cable terminals have been cleaned up, and I also decided it was a good time to clean the TB since I had the battery unhooked. Put it all together and it idles smoothly. Time will tell if the original issue is solved, but next time I'll replace the battery terminals, then the cables themselves. Won't be too long before we're ready for a new battery as well...they don't last long in Arizona heat.