Help: LBZ won't crank...TCM???
- Thread starter jrodd
- Start date
Wow I just read this and relized I need to read before I post lol You guys were all over it. But just wondering how well do these trucks run without a TCM? hard shifts or what all becomes ackward/unsmooth without the TCM?
Without the TCM, it won't start at all!!! no crank!!! When it all actually happened, my truck was running of course after I jumped the skidsteer...got back in the truck to move it and it wouldn't go into gear...shut the truck off and that's when it wouldn't start again...
So whats the point of starting the truck if it won't even move
not bshing you just thinking what good will it do you until you get a new TCM. I would think it would have some gears still
not bshing you just thinking what good will it do you until you get a new TCM. I would think it would have some gears still
So whats the point of starting the truck if it won't even move
The truck should function normally after he has repaired the lack of ground issue.
So its not a fried TCM, just a blown interal power fuse or something like that? Having it grounded with say a wire soldiered to the TCM and chassis would let it perform normal. Well then might as well save some money and keep it the way it is for a bit
It is a fried internal ground. the entire problem happened because GM did not ground the chassis of the TCM to begin with, thus causing the potential of having some external connection try to force ground through the TCM electronics and back through the vehicle wiring harness. Yes, the vehicle will operate like this, but it is not correct and can cause other problems down the road. a simple preventative maintainence tip would be to solder a ground to the TCM and connect it to the vehicle chassis before something like this happens.
Yes, I definitely plan on this being a temporary fix while I try to find a used unit...I just can't bring myself to spend $700 on a new one just yet!!!
Will it hurt the Allison driving it around with the TCM ground externally to the body? Cause mine will not engage the starter and my gear indicator light isnt working so it will not start...! Mine is an 06 lbz 6speed alli
I am always paranoid about jumping anything with my truck, this is why. Sorry to hear it but you came to the right place to get answers. :thumb:
Really? I drove my LB7 a few hundred feet without the TCM in at all. I had forgotten that I took it out until I put the truck in gear, and it shifted like crap. I drove it out of the shop and parked it just fine. No problem starting it, but the CEL was on the next start.
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i burnt my trans loom to charcoal on the weekend ( long story). started the truck with a screwdriver across the terminals on the starter as it wouldnt crank.. got limp mode and drove out of the bush.
Here is the info from GM---
Document ID: 2074199
#PIP3605A: CTC U0101
No engine crank and no communication with TCM
Feb. 29,2008
Models affected:
2006-2007 Chevrolet Silverado Classic
2007-2008 Chevrolet Silverado
2006-2007 GMC Sierra Classic
2007-2008 GMC Sierra
Equipped with Allison LCT-1000(RPO-MW7)Automatic Transmissions
Customer may comment that the vehicle will not crank or start/will not shift after vehicle has been jump started due to battery run down or after installation of after market equipment.Technicians may find no communication with the TCM and or DTC U101 [my PPE had only a C101,which I know isn't the actual DTC]stored in other modules.
A few TCM's have been returned from the field for analysis because of the above symptoms.The field returned TCM's were analyzed and found to have two battery ground nodes inside the TCM damaged by excessive electrical current passing through the heatsink of the TCM.The nodes affected described as wire bonds are wire tied to pins 9 and 69[battery ground pins] of the TCM.
The TCM is manufactured so that the heatsink of the TCM is isolated from all vehicle electrical systems including vehicle chassis ground.Do not ground welders,battery chargers,electrostatic painters or any other equipment to the heatsink.Disconnect the 80 way connector from the TCM when electrically welding etc. to the vehicle.
To avoid damaging the TCM in this manner,NEVER ALLOW the following:
1. Battery positive wires to touch the heatsink of the TCM[e.g.When jump starting vehicle]
2. Positive battery power chassis harness wire to pin 10 and pin 70 of the TCM to be wired without fuse protection of 10-15 amps.
3. Physical contact between heatsink and vehicle chassis or other ground circuit points.
4. Electrical grounding of devices such as arc welders,battery chargers,and electrostatic painters,or jumper cables to the TCM heatsink.
Recommendations/Instructions: Take the following steps to check for damaged ground wire bondsif the symptoms for a concern are ''No Engine Crank'' and/or ''No Communications'' with Tech II.
1.Switch ignition key off.
2. Disconnect the TCM electrical connector and remove TCM from the vehicle.
3. Test for continuity between pins 9 and 69 at the TCM.If continuity exists between pins 9 and 69,then refer to steps in eSI for ''NO Engine Crank'' and/or ''No Communications''
If the circuit between pins 9 and 69 have no continuity,then the TCM has been damaged/shorted from some sort of external source shorting to the heatsink of the TCM.
1. Inspect for the source that shorted the TCM heatsink.
2. Eliminate or repair the source or condition that caused the damage.
3. Replace damaged TCM after the condition that caused the TCM damage has been corrected.
NOTE: Visual surface pits and carbon deposits are typically found on the TCM heatsink when high energy arcs are generated by shorts between the heatsink and battery power.
__________________
Document ID: 2074199
#PIP3605A: CTC U0101
No engine crank and no communication with TCM
Feb. 29,2008
Models affected:
2006-2007 Chevrolet Silverado Classic
2007-2008 Chevrolet Silverado
2006-2007 GMC Sierra Classic
2007-2008 GMC Sierra
Equipped with Allison LCT-1000(RPO-MW7)Automatic Transmissions
Customer may comment that the vehicle will not crank or start/will not shift after vehicle has been jump started due to battery run down or after installation of after market equipment.Technicians may find no communication with the TCM and or DTC U101 [my PPE had only a C101,which I know isn't the actual DTC]stored in other modules.
A few TCM's have been returned from the field for analysis because of the above symptoms.The field returned TCM's were analyzed and found to have two battery ground nodes inside the TCM damaged by excessive electrical current passing through the heatsink of the TCM.The nodes affected described as wire bonds are wire tied to pins 9 and 69[battery ground pins] of the TCM.
The TCM is manufactured so that the heatsink of the TCM is isolated from all vehicle electrical systems including vehicle chassis ground.Do not ground welders,battery chargers,electrostatic painters or any other equipment to the heatsink.Disconnect the 80 way connector from the TCM when electrically welding etc. to the vehicle.
To avoid damaging the TCM in this manner,NEVER ALLOW the following:
1. Battery positive wires to touch the heatsink of the TCM[e.g.When jump starting vehicle]
2. Positive battery power chassis harness wire to pin 10 and pin 70 of the TCM to be wired without fuse protection of 10-15 amps.
3. Physical contact between heatsink and vehicle chassis or other ground circuit points.
4. Electrical grounding of devices such as arc welders,battery chargers,and electrostatic painters,or jumper cables to the TCM heatsink.
Recommendations/Instructions: Take the following steps to check for damaged ground wire bondsif the symptoms for a concern are ''No Engine Crank'' and/or ''No Communications'' with Tech II.
1.Switch ignition key off.
2. Disconnect the TCM electrical connector and remove TCM from the vehicle.
3. Test for continuity between pins 9 and 69 at the TCM.If continuity exists between pins 9 and 69,then refer to steps in eSI for ''NO Engine Crank'' and/or ''No Communications''
If the circuit between pins 9 and 69 have no continuity,then the TCM has been damaged/shorted from some sort of external source shorting to the heatsink of the TCM.
1. Inspect for the source that shorted the TCM heatsink.
2. Eliminate or repair the source or condition that caused the damage.
3. Replace damaged TCM after the condition that caused the TCM damage has been corrected.
NOTE: Visual surface pits and carbon deposits are typically found on the TCM heatsink when high energy arcs are generated by shorts between the heatsink and battery power.
__________________
I know this is an old thread but it saved my ass lol
I have a 2010 lmm... I did the bandaid for a while and it drove, just shifted kinda hard.. One day I was driving and stopped at a gas station went to start it back up and nothing happened..(my first time soldering skills didn't hold up) anyway I had someone help me start the truck while I held the grounded wire to the Tcm and it started but due to not having the solder with me I left the wire hanging until I could get it home.. When I got back in the truck I had no line under PRND to indicate whether I was in park reverse drive etc. but it drove to the house and I didn't drive it again until today when I went and found a Tcm at a junk yard.. I changed it out and truck starts no problem and will go into reverse and drive but still no indicator as to what I'm in (reverse,drive,etc.) I have not drove the truck around yet cause I needed to get to work I just backed it out if the drive way then pulled it back in.. I'm curious if it might be the neutral safety switch? Any thoughts?
I have a 2010 lmm... I did the bandaid for a while and it drove, just shifted kinda hard.. One day I was driving and stopped at a gas station went to start it back up and nothing happened..(my first time soldering skills didn't hold up) anyway I had someone help me start the truck while I held the grounded wire to the Tcm and it started but due to not having the solder with me I left the wire hanging until I could get it home.. When I got back in the truck I had no line under PRND to indicate whether I was in park reverse drive etc. but it drove to the house and I didn't drive it again until today when I went and found a Tcm at a junk yard.. I changed it out and truck starts no problem and will go into reverse and drive but still no indicator as to what I'm in (reverse,drive,etc.) I have not drove the truck around yet cause I needed to get to work I just backed it out if the drive way then pulled it back in.. I'm curious if it might be the neutral safety switch? Any thoughts?