LB7: No crank/no start/ no wts light
- Thread starter Canadaguy
- Start date
TCM -- on fan shroud, you cant miss it
ECM -- in front of drivers side front wheel, inside of frame.
You need to go back and recheck everything you did under the truck. You either did something to a wire harness/ground when under there doing the trans, or you have another problem thats completely unrelated. Have you checked (not just visually) the grounds like the guys said? Have you checked the harnesses going into and out of the underhood fusebox? Double checked all fuses?
ECM -- in front of drivers side front wheel, inside of frame.
You need to go back and recheck everything you did under the truck. You either did something to a wire harness/ground when under there doing the trans, or you have another problem thats completely unrelated. Have you checked (not just visually) the grounds like the guys said? Have you checked the harnesses going into and out of the underhood fusebox? Double checked all fuses?
I went through the fuses they all appear ok, i have gone through and the wite harness looks good into the fuse block. I cannot figure out how to get the fuse box off? To check underneath of it. I got the truck with tranny pulled back already ive tried to locat e and all wires look good and hooked up. Hate trying to retrace other ppls work.. i take oics of things i take apart. This is turning into a nightmare! Gonna try the ground on the tcm and climb back under and check wires again.
Ok update: pulled fuse block off all looks good. No rubs no broken wires. I boughr a light tester, tested all fuses under hood and are good. Climbed under the truck and checked the connections at the transmission all are ok. As a recap:
No data on my dash in the display-kms etc
No gear indicator light
No wait to start
No stereo power
No power to the edge module
No crank
I have power to the starter, nothing to the ignition.
Passlock light comes on, shuts off and then turns back on.
The black plastic ring that goes around the ignition tumbler has broken off(thepiece that pushes the two nobs down) could that be my problem?
No data on my dash in the display-kms etc
No gear indicator light
No wait to start
No stereo power
No power to the edge module
No crank
I have power to the starter, nothing to the ignition.
Passlock light comes on, shuts off and then turns back on.
The black plastic ring that goes around the ignition tumbler has broken off(thepiece that pushes the two nobs down) could that be my problem?
Might have to i guess. Wont it need to be relearned for the edge? Have a mechanic going to come and look at it. I cleaned the grounds in the chasis just now, checked for power at the neutral safety seitch and transmission, its getting power. So not sure what else i can check? Does anyone know what wires to prob for power on the ecm?
Still havent found any solution to this problem. Going to try and probe the wiring for ecm/tcm/bcm through the harnesses to see where the power loss is. It seems to me that the ignition is not giving the signal to start and that its not receiving the info from the computer. Any tips or things i should check first would be greatly appreciated.
You need access to the wiring diagrams and then just take your time and go through everything.
If that much of the cab isn't getting power, I would look at the wiring that feeds the ignition switch, and the fuses. It could be the big square fuses, which have to be removed and tested through the bottom (though often you can visually see they are blown).
The neutral safety switch will only prevent a crank, it won't stop the dash from powering on or the wait to start light. The wiring on these trucks seems needlessly complex, but once you've spent enough time with the diagrams, you start to see how it all works together and how what GM did saves them time/money building the harness.
Just keep at it, there is no easy answer. Work through the diagrams and find where the power stops flowing. Good luck.
If that much of the cab isn't getting power, I would look at the wiring that feeds the ignition switch, and the fuses. It could be the big square fuses, which have to be removed and tested through the bottom (though often you can visually see they are blown).
The neutral safety switch will only prevent a crank, it won't stop the dash from powering on or the wait to start light. The wiring on these trucks seems needlessly complex, but once you've spent enough time with the diagrams, you start to see how it all works together and how what GM did saves them time/money building the harness.
Just keep at it, there is no easy answer. Work through the diagrams and find where the power stops flowing. Good luck.
Thanks, above post seems correct. I have found the whole wiring package on https://www.gmupfitter.com/publicat/2004_BB/2003_Beyond_LD_Electric_CK.pdf
On another thread. It has a large 300+ page of wiring for all theae trucks. Will be going through again. Replaced the broken lock cylander and now have power to the stereo. I did an edge delete thinking maybe it was an issu. Someone said try an ecem which is what i am thinking. But not 100% sure on the whole trsting wires and how to start doing this. Will keep it updated as i go.
On another thread. It has a large 300+ page of wiring for all theae trucks. Will be going through again. Replaced the broken lock cylander and now have power to the stereo. I did an edge delete thinking maybe it was an issu. Someone said try an ecem which is what i am thinking. But not 100% sure on the whole trsting wires and how to start doing this. Will keep it updated as i go.
Sounds to me like you have a power distribution block that's not properly engaging all the circuits. You're BCM is definitely not powering up. That could be as simple as a bad ignition switch. You need to scan for codes and see what's coming up. If the BCM isn't communicating you will get codes for that.
Well well well... what a wierd day. Spent the night learning about the ignition system wiring and the glow plug wiring. Spent 10 seconds looking at the fuses and realized that someone prior to me buying the truck removed the bcm fuse.. was not in it at all. Put that in and voila it cranks.. powers up to the dash, glowplug circuit has power. I have a no start condition now. I have no sound coming out of my stereo. Door chimes not working either. I replaced the broken ignition tumbler and it came with a new key. How do i do the relearn function properly on an 03 lb7. I am hoping that this is it. Currently rechecking all of the fuses. What a nightmare for something so stupid i was kicking my ass all morning!
