Electrical Gremlin.. UBEC??

GMJim · September 10, 2012

Hello all. I'm new to the forum and see there is quite a bit of a knowledge base here. Hopefully I can repay the favor if I can get some help with my issue. I've been chasing a electrical gremlin in a 2011 Suburban and am looking for some ideas. This truck is fully optioned and is in otherwise perfect condition and has low mileage. The problem is the vehicle will suddenly just shut down. Everything will quit. Engine and all electrics cut out (Kinda scary on the highway at 70mph!). Then from time to time the remote key fob won't activate the locks. Some times while driving down the road the locks will lock and unlock several times, the radio will turn on and off and the gauges will go in fits with needles bouncing back and forth. Now I don't consider myself an electronics expert but I've been fixing GM cars for nearly 40 years and this one has me stumped. Before you blame the battery or battery connections, I've checked and cleaned EVERYTHING! Sometimes you get in to start it and nothing? Wait a few minutes without doing anything and bingo, it starts? There are NO CODES. I think it may be a power or ground issue to the PCM or BCM but haven't had time to really get into testing everything. I'm going to spend a few hours with the scanner next week to see if I can duplicate the problem and start checking harnesses. Three GM dealers have all tried but failed to even zero in on this issue. Looking for some ideas that I haven't thought of.

Suggestions (useful ones please) are very welcome.

Jim

rdnkcpa · September 11, 2012

If it is under warranty and the dealers can't fix it, Lemon Law that sucker. Make it GM's problem.

asc08 · September 11, 2012

Sounds like you are on the right track by checking connections. Check all grounds as well.

I would not rule out a battery that has an intermittent internal short. Before buying a new battery, you may want to try it with a known good one.

The engine failure sounds like a PCM issue, and the locks sound like a BCM issue. You may want to start with the common connections (power, grounds) for those two. I would be surprised if both modules were bad.

8.1HD/ALLISON · September 11, 2012

+1 on above. Possible ignition switch intermittenly open?

GMJim · September 13, 2012

Thanks for the replies evryone. I think the ignition switch can be ruled out because the keyfob lock/unlock feature will fail to work from time to time as well. I'll be checking all the grounds and the UBEC when I get time.

I recently put a factory fog light kit in my wifes Volvo C30 (her choice not mine). $135.00 not bad I thought. When finished they wouldn't work??? Called the parts department to find out if they had any defective ones show up. The answer was no but did you buy the software with it?..............Software? Yeah the software is $35.00. Oh so I just put a disc in the entertainment center (they don't call it a radio anymore) and it will program the lights? Ah, no........ Ya hafta bring the car in and we hook it up to our worldwide computer system and download the software to the car. That's a minimum 1 hour labor $110.00 plus the software. I used to fix cars. Now I'm fixing rolling computers with more airbags than a blimp!

Sounds like you are on the right track by checking connections. Check all grounds as well.

I would not rule out a battery that has an intermittent internal short. Before buying a new battery, you may want to try it with a known good one.

The engine failure sounds like a PCM issue, and the locks sound like a BCM issue. You may want to start with the common connections (power, grounds) for those two. I would be surprised if both modules were bad.

Shouldn't the vehicle continue to run off the alternator if the battery power is lost??

asc08 · September 13, 2012

"Shouldn't the vehicle continue to run off the alternator if the battery power is lost?? "

I think those days are over. A battery with a cell going bad, may cause a drop in voltage and start making the computers go nuts.

A friend of mine had an older suburban, sometimes it would run fine, sometimes it would not start. Sometimes it would die, other times it would run really rough. No codes. He went over it with a fine tooth comb and came up short.

Took it to the dealer, and after a good bit of looking, the replaced the battery and all was well with the world. What steered him away from the battery was that when it started, it started fine, cranked hard.

GMJim · September 21, 2012

Dealer tested the battery cables and reported the positive cable had resistance????? Anyway replaced the cables and so far so good. What are they making these cables out of these days?