Odd Electrical Problems

formulator · August 28, 2009

Got an '03 yukon that all of a sudden started doing odd things today. When I go over bumps the service brake system message comes up and the red alert light and abs light comes on. At this same time that check engine light comes on briefly and the doors lock or unlock. After I'm back on smooth road the red alert and abs lights stay on but the rest of the odd behavior stops. Also, once when there was a bump at a stop sign the truck also stalled. Seems like some of the vehicle losses power when going over bumps. I figured it must be a ground bad or possibly the ignition switch. I've cleaned 4 grounds (one high on driver firewall, 2 under driver seat near when frame mounts to body and one behind the front bumper on the driver side) and that hasn't helped. I'm going to go over the wiring under the dash next but was wondering if anyone had any ideas.

Thanks,

Colin

rjirvine · August 29, 2009

Have you checked the main ground from the neg battery cable and the terminals on your battery? Engine ground strap and alternator wiring connections? Also, check to see if your fuses are tight, I had one that was somewhat loose and drove me crazy until I found it.

98 Z71 SLT · August 29, 2009

You have 2 main grounds right underneath the driver door...crawl underneath and pay close attention the the frame. You will see a bunch of grounds bolted to the frame...right in the area of the driver's door. Take them off, clean them up, reassembly the grounds, and take it for a ride.

formulator · August 29, 2009

Thanks for the replies. I've tried all suggestions and still the problem persists. Anyone know where the BCM located and if could it cause these types of issues? Today when I tried to start it I had trouble, it would turn over and start then run really rough and die then it wouldn't turn over, after a bit i tried it again and it started and is running fine again. I thought that was pretty suspect of bad battery/alternator connections but I've looked at those and they all seem fine.

I don't get what would cause the door locks to go all crazy when I go over bumps. They lock/unlock rapidly and it seems totally random. The truck has an aftermarket alarm and also a mandatory insurance company immobilizer. Maybe it's something to do with that?

BTW, the computer has no codes just the ABS light which I can't seem to check with the scanner I'm using. I'm confused as to what to try next. Any suggestions appreciated.

Thanks,

Colin

formulator · August 31, 2009

I managed to figure this out today and just wanted to post the solution for anyone else that might run into this thread.

Today I had trouble starting the truck but not as bad as the previous day. I had the another look at the wiring under the dash and couldn't really find anything. I decided to go for another test drive and this time the truck stalled and wouldn't restart. Luckily I was only a block away from home so I left it for a bit and came back to it later, again I had issues getting it to start eventually. After wiggling a harness on the passenger valve cover the truck started and I drove it home. So, started to look at this harness a little closer, it's a harness clipped onto a bracket above the valve cover on the pass side that eventually hooks up to the coil packs on that side of the engine. It seemed that moving these wires would allow me to start the truck I eventually traced the wires to the back of the engine block where they met other wire conduits, one of them the conduits had a single black/white wire in it that was severed hanging down onto the block. Once I grounded that wire the truck started and ran no problem. Because I couldn't easily get to the back of the block to reground in the same location it was in I just soldered on a longer wire and grounded the wire to the engine block ground high on the driver side firewall.