no idea probably takes a programmer
Motor refresh complete, now no crank, no start
- Thread starter nadthomas
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Perhhaps the wording from the dealer was out of sort or he misunderstood. I found a gm bulletin last night that specifically addressed that removing power from the onstar module will cause the module to go into a backup battery drain that cannot be reversed and will require an entire new onstar module. One of the vehicles listed was yours, the module including incorperated backup battery is behind your radio.
I know for sure they put a new bcm in and flashed it to solve the guys problem that sounds exactly like yours. Perhaps they figured the failure of the bcm was caused by onstart backup power supply draining since they are tied together electronically.?
You are correct, there is no battery inside the actual bcm, sounds like the wording of the issue was either off, or got lost in translation. There was indeed a keep alive onstar battery source that drained that was designed to allow onstar to communicate with you and the functions of your vehicle in a crash though.
Hopefull your ecm fixes it, but you know where to point the mechanics as another possible issue if it doesnt.
I know for sure they put a new bcm in and flashed it to solve the guys problem that sounds exactly like yours. Perhaps they figured the failure of the bcm was caused by onstart backup power supply draining since they are tied together electronically.?
You are correct, there is no battery inside the actual bcm, sounds like the wording of the issue was either off, or got lost in translation. There was indeed a keep alive onstar battery source that drained that was designed to allow onstar to communicate with you and the functions of your vehicle in a crash though.
Hopefull your ecm fixes it, but you know where to point the mechanics as another possible issue if it doesnt.
can you provide a link to this bulletin?
Too many games on to dig it up, but its out there. There is plenty of general information on the failure to turn the key off before unhooking the battery. I will check around later for the specific to bulletin that says the same inclusive of your suv.
Perhaps the series of events is more the cause than anything. Maybe hooking up the power with the engine out and all the harness grounds unhooked wrecked the bcm or something. Not sure if its that, or the onstar battery running down that does something to the bcm, but the similarity is uncanny.
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nadthomas
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Not to take away from the discussion on the BCM, but while i was waiting for the replacement ECM I decided I would use today to button everything else up. This just involved putting the trans pan back on, filling up the trans, slapping the front bumper and headlights back on, and putting in the wheel well splash guards. Decided to check to see if it would start on last time, and found no gear indicator on the dash again. Verifed with Tech2 no communication with TCM. Gaaaahhhhhhh. 
thompsoj22
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Extremely valuable info for a diy'er like me!!! thanks for all the headaches that i could have incurred through a lack of knowledge. Forum's rock!
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nadthomas
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New ECM arrives Friday!
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nadthomas
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So the new ECM did not fix the problem. I believe I may be dealing with a Canbus/Wiring issue. The canbus has 2 terminating resistors of 120ohms if you put an ohm meter across pins 6 and 14 on your ODBII port you will be measuring both resistors in parallel so you should get 60 Ohms. I am seeing 120 ohms, which means I am only seeing one of the two resistors. Which also means either one of the resistors is bad, or I have some bad wiring. Well, one of the resistors in internal to the ECM, so if I disconnect the ECM I'm going to continue to see 120 Ohms or 0 Ohms. So, I disconnected the ECM and still got 120 Ohms. Which confirms that the other terminating resistor is good. I then verified on both my old and new ECM that I had 120 Ohms on pins 27 & 28 on the C1 connector on the ECM itself. So, the internal resistor in the ECM is good, I'm just not seeing back at the ODBII port. From the diagrams I could find, it looks like the next connection on the Canbus after the ECM is the TCM. Since I lost communication again with the TCM I suspect my problem lives between the ECM and TCM. Eitherway, I don't have access to all of the write wiring diagrams, and don't have the tools to make probing out these connections easy. So, I will be getting it towed this week to a shop to diagnose. I'll let you all know what was found in the end.
Not sure how competent the shops are around your parts, but you sound like you have more ability to fix the problem than almost all but the dealership themselves. Hopefully you bte the bullet and take it to gm, this will surely be one of the situations when paying more per hour, ends up with a smaller bill.
