Truck started having starting issues a few months back and eventually after repeatedly turning the ignition key it would start. Later it did this to me again only this time it was in my driveway and I could not get it to start at all. I got my mechanics degree from the University of YouTube and turned to it to help resolve my issue and I did find a video where it turned out the fuse #34 the DLIS fuse was the culprit and sure enough mine was blown and once replaced it started up and all was good. Anyway I figured this could happen again so I purchased extras just to have on hand and it did happen again only this time it blows it immediately once the key is keyed to the on position.

I've been chasing what I believe is short to ground and have traced the wire with the help of a wiring diagram and have ruled out the ignition switch and the theft deterrent module. I was able to get at the BCM and disconnect it and not get a blown fuse however my security light continues to stay on causing a no crank issue. Why they designed the ignition and fuel injection system to give the command to start and send fuel through this device makes zero sense to me. Electronics can fail and when they do you can find yourself stranded on the side of the road. Electrical is not one of my strong pponts but through trial and error I've found that the fuse blows once the black connector on the BCM is plugged in and the key is powered on. I feel I'm getting closer to the root cause of the problem and looks like I'll be searching for short to ground on that circuit now but cannot rule out that the short is occurring inside the BCM. If anyone has ran into this issue or you have any suggestions you wish to share I'd appreciate it.

Thanks, Roger

 

I'm done with trying to figure this out, it's time to call in the hired guns.

 

I am not a fan of the GMT900 trucks. That being said it very well could be the BCM on that truck. At one point they were only like $100 new because they were replacing so many. The problem is they have to be programed to the vehicle.

Earlier this year my fathers 07 rolled down the front driver side window, it wouldn't roll back up. I bust out the scan tool and you can see the command from the switch to go up and down. Hmm the window motor must have died. Because all the wiring is stationary in that part of the door. Let's get the power probe out and test the window motor. Nope. Goes up and down like it supposed too. Ok lets check the circuit, maybe the connection is bad or something? Look up the wiring diaghram and of course the wire colors are wrong... Stupid 1st year of production problems... So I had to use the pin locations and back trace the wires because If I remember correctly it goes through the BCM. Finally I am able to confirm circuit integrity and load test the wire's. Thats good. Ok must be the switch. Call the dealer, got one on order, It shows up a few days later. They inform me it has to be programed in order to function. No Problem, I will get a 3day subscription to AC Delco Tech Connect and do it my self. Nope! After setting everything up I get an Error and The Vin Can not be found must contact the Service center with a code and provide the Vin. I guess GM Switched over to a new system and the new system required manually transferring all the data. So they only transferred a certain a amount of vehicles. Any way after them updating a driver or something on my end and confirming the Vin in the Vehicle, They had to get a different person on the call so he could transfer the files for that vehicle into the new system so I could down load the software for the switch.

Once I was able to program the new switch, It works fine.

But the damn switch was was around $200 plus the $45 on the Programing. I feel like if I had a shop do it, It would have been at least a $500 repair.

 

Yeah I just don't have a scan tool or even the knowledge on how to use them as all of this electronic technology is above me. I haven't found a short to ground on that wiring and according to the wiring diagrams it comes from the fuse block through a J212 splice then into the ignition switch and theft detterent module then from those into the BCM which leads me to believe it's going to ground somewhere inside the BCM and that's what's causing the issue. I can get one shipped for about $200 and they just need the VIN to program the part before shipping out.

Also wondering if the fuse block could be causing the DLIS fuse to blow because the fuse connection there is not very good. I'm thinking if I powered that wire with an inline 2 AMP fuse and it still popped I could rule out the fuse block as the culprit. I've visited all my grounds to make sure they were clean and tight and I'm at that point where I could do something stupid like throwing parts at the problem but going down that rabbit hole gets expensive real quick. I'm already $500 in but the truck needed a new battery and nothing like a good excuse for buying some nifty diagnostic tools to add to my collection.. Luckily I know someone I can trust who's not going to rake me over the coals and I'll be getting this towed out my driveway and out of my sight for awhile.

 

Update: Went by his shop and explained to him what was going on and he aksed if the fuse blows with the run crank relay is disconnected and I told him I wasn't sure. He said check that out because if the fuse is blowing with the relay in then it's most likely not the BCM and there's an issue on that wire but if it blows with the relay out then it's shorting out in the BCM. Well it blew the fuse with the relay out and turning the key to the on postion so it looks like I'm in the market for a new BCM.

 

Right on. Sounds like he has delt with that before. Let us know if that fixes your issue.

 

Guys this truck has me so confused..I don't hink it's the BCM now but what the hell do I know. What I've determined is that I'm not getting a connection from fuse #35 to the connectors for theft deterrent module or the ignition switch. It has continuity from the component side of the fuse to the power wires but I was not getting a 12V reference to the connectors for those modules. This explains why it didn't reckgonize the key and the security light just stayed on...Anyway I made a jumper wire with a 2 AMP in-line fuse between there and was finally able to get a 12V signal to those connectors that powered the components and to my amazement the security light went away and it finally started but immediately died. I started it again and it died again so after the third or fourth try it started and ran where I let it run for a few minutes and I decided that now would be a good time to reposition the truck so I backed it up and pulled back up on level ground and it died again.

I've had this truck for six years with zero problems up until now but I tried starting it again and after a couple of attempts of starting and shutting down it finally started and kept running. I was thinking to myself what could be causing it to stall out and as I went to put my hands on the key I wiggled it some and the truck shut down again. Hmmm...Could it be a worn out ignition key tumbler or is the key sensor on the ignition switch causing this issue? The good news is that the key is now communicating and it will turn over so the BCM I just purchased will probably be another part waiting to be used at a later date.

 

Fuse block and Transmission Control Module.

$3400 dollars later and my truck will be up and running again.... Now just to get the insurance company to send more than $5600 to replace my damn roof. I pay those bastards like 2K a year and been with them for 20 years and that's all they want to pony up.. I've gotten several estismates that all range from 13K-17K to replace the roof and I'm hoping to only come out of pocket around 4K to get it fixed. What little bit of Savings I did have will be taking a hit and man would it have been nice to invest that $$$ into a rod/piston swap and a customized ProCharger kit for the LSX427.