ive run into the similar problem several times being an automotive mechanic, what i have found on most cases is the side post battery cables cover wont let the ground ground, so i trim the plastic cover that contacts the battery, or just remove it totally. let me know if this helps.
Motor refresh complete, now no crank, no start
- Thread starter nadthomas
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nadthomas
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Possibly.....after pulling the motor I reconnected the battery so I could roll it out out of the garage to degrease the engine bay. While doing that I know there were a couple of disconnects/reconnects. I honestly don't recall at this point if the key was ever left on during that.
In your experience did that fry the ECM?
Ran into this with a customer that did an engine swap on his nnbs silverado. He was moving it around his shop and at some point unhooked the battery while the key was on. I went to try and figure it out/tune the new engine and couldnt communicate with the truck. Turns out there is an internal keep alive power source so if you get in an accident data can still be accessed via onstar. So say for example your battery gets ripped out in a hard front end collision, onstar will still be able to see whats going on. If you unhooked the battery while the key is in the on position, it activates the backup power source and runs it until its dead. Once the internal source is dead its screwed.
It was a while ago so i texted buddy and he said it was the bcm gm replaced and flashed. Gm knew the exact cause of the problem so maybe call your local dealer just to be sure before throwing good money around. It was 100 percent the same problem though.
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nadthomas
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Interesting. If that is the case, then I would expect that if I did a little more digging with the Tech2 looking more at the BCM that I would find some sort of error, or something.
Possibly. Gm only charged him a half hour they nailed it down so fast. Didnt even take it off the trailer so you may have the power to figure the same.
They did say once the power is drained on the bcm it is bricked though, so if you get down that hallway and find the bcm power is the problem it needs to be replaced.
We actually had a bcm from a wrecker as the last straw that we took in with the truck to get programmed to the vehicle, it was then that the gm tech told buddy of the reason for the failure of the first bcm. I have gotten a few more texts clearing up the details. The bcm has the keep alive power that powers up the various components for onstart to work on a power outage.
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nadthomas
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I finally got a chance to get back out to the garage tonight, and went back over all power/ground and ECM connections. Decided just to order the pre-programmed ECM. The seller has a 14 day return policy and only a 20% restocking fee. So, worst case if it doesn't fix my problems I'll probably just have the Denali towed to a shop with both computers and hopefully the shop can get it figured out in less then 2 weeks. If the ECM wasn't needed then I'll just send it back. Unfortunately, I have other things I need to focus my time on. So, I might have to hand this off to someone else.
Good luck with this. I’m really curious as to what the problem is.
