Gremlins

[Bag-a-bolts]

This started two weeks ago. My Truck is a 2003 GMC Sierra 3500 6.6 LB7 CC Dually.

 

The fuel, volt, oil, temp and trns temp gauges shut off and the service 4wd message appears in the message center and the 4X4 buttons all light up, this is usually followed by the message driver 1 and the chime, like a start up cycle. The little line under the gear selection dissappers as well. The radio is also effected and is randomly turned on and off, also the power window and lock controls lose function intermittently. Sometimes the entire cluster doesn't turn on as if not responding to wake up. The dimmer control, dome light, passlock & fob are also losing function, often when opening with the key the horn goes off as if I am breaking in. On the cluster the Batt light is constantly on.

Also the Ignition doesn't act normal, it doesn't always recognize the key is in and the door is open. When turned to Acc radio & windows actived for e few seconds at a time. Turn key to run and cluster turns on but voltage and temp guages don't read, no radio or windows work here either. Turn key to start and the truck fires up, runs and driver normal.

 

The following don't seem to be effected these work as normal in normal key postions.

Wash & Wipers

HVAC & Blower

Headlights HI LO & Fog

Rear Window Buttons

Rear Def

Power Mirrors

Cargo Light

 

What I've done since this started -

 

Replaced batteries and checked for corroded connections

Inspected harnesses for chaffing and altered position by hand to see if any effect on problem - nothing

Checked fuses and conections related to IPC TBC DDM PDM TREC

Checked and cleaned ground under drivers side door. It's grounded.

Checked voltage at various points in cab 12.6 v stopped 14.6 running

 

What I suspect from what I've read -

 

Bad Ignition switch Or Bad TBC

Low voltage to TBC or related modules

Short in the harness

 

Has anyone experienced this problem before? Since this all occured in a short time period I'm sure it is one issue causing it.

 

Any suggestions would be very appreciated.

[bill190]

For this I would get a factory service manual and wiring diagram if you don't already have it...

 

Then take one thing at a time and read all you can about it. Learn how it works, where it gets its power from (which fuse/circuit).

 

Then find the power wire for that circuit and attach a multimeter to monitor that wire. Just leave the multimeter in the truck and see what it is reading when this happens.

 

So to start, monitor the power to these things. See if power is being lost somewhere.

 

Then if power OK, learn if there is an electronic module which supplies the information to all these things. Monitor the power to that.

[L29er]

I would certainly get that vehicle scanned, there could be codes thrown from the instrument cluster (yeah there is a computer in there!) It could very well pin-point the problem, if not, get the instrument cluster re-flashed, it can be done at the dealer or a shop with the right computer software, the shop i used to work at could re-flash them and usually clear up cluster problems, its hard to say if all your problems are caused by the cluster but its a place to start after all the things you have done so far. Also don`t be surprised if they say the cluster is NFG! its very common, they can be found fairly affordable (compared to dealer) at places online, (sometimes ebay) then they just need the mileage installed at a dealer (unfortunatly) but anyways might be getting ahead of myself here, Get that baby scanned and go from there, Those electrical gramlins can be a PITA!

[Bag-a-bolts]

Well I was almost ready to give this one to the dealer but I thought I'll check just a little more, I pulled the trim off the sill area beside the drivers seat and noticed things were quite damp. I followed the harness on the floor up under the drivers seat, I unbolted and pulled the seat to inspect the rest of the harness. I found the cause of my problem and I imagine it would likely occur with age in other trucks in winter areas so I'll post what I found. The Problem starts with salt and snow/water in the foot well area. The felt under the carpet gets saturated and wicks moisture up under the driver seat, the air bag system is under the driver seat carpet on the metal cab floor. As the cabin heats up the module stays cold and creates the perfect setting for some serious condensation, which with salt becomes serious corrosion. If you have a work truck that has seen its share of slushy boots and are having some strange electrical issues, check the module under the seat. It was the source of my problems.

The module was covered in white flaked aluminum and salt. At first I thought it just looked bad but may still work because the connector was perfectly good, no corrosion inside the connection so I cut open the module to be sure this was really it. Tried the truck with module disconnected and all the problems were gone.

Hope this thread helps someone.

[L29er]

WOW good find!!!

[bill190]

Good detective work! (And salt water is an excellent conductor of electricity...)

 

I say: It is always something simple, but finding it is the hard part!

[Draenor]

The airbag module? wow wouldnt of guessed it..BCM yes, but not this. I wonder if you could get a good short in that module and set off the airbags. (could be deadly)

[Bag-a-bolts]

I priced the module today, 850 plus tax from the dealer. 250 from local salvage special order. I choose to go used. When I get it I'll install it and head to the dealer, these modules needs to be programed by a tech 2 with the right software to be recognized - .5 hrs at the dealer.

 

Now I just got to free up that seat belt lol!