Help: LBZ won't crank...TCM???

[jrodd]

Hey guys...long time member over at Diesel Place, finally joined over here!!! I've been a watcher for awhile, but this is my first post as I am having problems with my LBZ and there seem to be much more knowledgable folks over here!!!

Here's the story...

A couple days ago I used my truck to jump start my skidsteer and since then, it won't start!!! I have power in the dash and all, but no crank. My dash says "CHECK BRAKE SYSTEM" and I am getting a C101 code with my PPE. I also don't have the gear indicator light (P, R, N, D, etc) with the key in the ON or RUN positions. I have checked all fuses and all are good. I referred to the starting system schematic and started tracing things...I have power from the ignitions switch to the 10A crank fuse and then on to the TCM, but no power coming out of the TCM where it should be!!! I also jumped the starter relay and the starter does crank, so the starter's good...any thoughts?? Did I fry my TCM, or is this not necessarily the case???

Thanks for any help guys, and if this should be moved to another area, don't hesitate!!! I wasn't exactly sure where to put it....

Thanks again!!! I want to try to get this thing fixed myself rather than taking it to the dealer!!!

 

[MMLMM]

ground the TCM case to the chassis/ground and try cranking...

if it cranks, you fried the circuit in the TCM

 

[Mike L.]

For all you guys out there, jump starting is a thing of the past. Don't do it unless you are ready to pay a price.

 

[Josh2002cc]

Please explain Mike.

 

[jrodd]

And you'd better believe I won't be doing it again!!! Especially with my truck!!!

I will try grounding the TCM in the morning...just ground the unit itself??? I have it pulled loose from it's mounting point...what if I just lean it over to the ground post at the B+ terminal and hold it there while cranking?? LOL...this sure sounds like if it's not fried already, it will be after this!!! haha....

 

[Mike_S]

For all you guys out there, jump starting is a thing of the past. Don't do it unless you are ready to pay a price.

Yes, please do explain further. I have used my truck to jumpstart a multitude of vehicles, from ten wheelers to John Deere tractors to four wheelers...never had a single problem. I'd be interested to hear your theory on this one.

 

[Bryce418]

the crank signal is sent from the 10a fuse to the tcm and ecm, the ecm is where the relay coil is powered from. i'm going to guess the issue is the tcm is fried or theres a blown fuse somewhere or you let the magic smoke out of it,there is the possibility the ecm is kaput too. I have replaced a couple ecm's for no start issues, but with the no prndl display I'm leaning towards an issue with the tcm or a comm issue.

 

[66impala]

Hey guys...long time member over at Diesel Place, finally joined over here!!! I've been a watcher for awhile, but this is my first post as I am having problems with my LBZ and there seem to be much more knowledgable folks over here!!!

Here's the story...

A couple days ago I used my truck to jump start my skidsteer and since then, it won't start!!! I have power in the dash and all, but no crank. My dash says "CHECK BRAKE SYSTEM" and I am getting a C101 code with my PPE. I also don't have the gear indicator light (P, R, N, D, etc) with the key in the ON or RUN positions. I have checked all fuses and all are good. I referred to the starting system schematic and started tracing things...I have power from the ignitions switch to the 10A crank fuse and then on to the TCM, but no power coming out of the TCM where it should be!!! I also jumped the starter relay and the starter does crank, so the starter's good...any thoughts?? Did I fry my TCM, or is this not necessarily the case???

Thanks for any help guys, and if this should be moved to another area, don't hesitate!!! I wasn't exactly sure where to put it....

Thanks again!!! I want to try to get this thing fixed myself rather than taking it to the dealer!!!

ok this is going to sound strange. but put your key in the run post like your truck is running. then just see if the shifter will go in to rev, or drive with out placing your foot on the BRAKE. if it does this you need a ign. switch. on the column. if it doesn't do that then check your grounds and fuses. im think its the ign. switch again make sure you dont put your foot on the brake. to see it it shifts.

 

[66impala]

Yes, please do explain further. I have used my truck to jumpstart a multitude of vehicles, from ten wheelers to John Deere tractors to four wheelers...never had a single problem. I'd be interested to hear your theory on this one.

i jump start someone about every 2 weeks and i dont have problems. i havent been able too sence someone ran in the passenger side of me and the body shop has it. dont even know if im going to get it back. its pretty bad i here.

 

[duramaxxin]

Im thinking its the TCM the exact same thing happened to a buddies 06 LLY.

 

[jrodd]

ok this is going to sound strange. but put your key in the run post like your truck is running. then just see if the shifter will go in to rev, or drive with out placing your foot on the BRAKE. if it does this you need a ign. switch. on the column. if it doesn't do that then check your grounds and fuses. im think its the ign. switch again make sure you dont put your foot on the brake. to see it it shifts.

The truck WILL NOT shift from PARK without my foot on the brake, works fine with my foot on the brake though...check this one off the list...thanks for the help!!!

 

[jrodd]

the crank signal is sent from the 10a fuse to the tcm and ecm, the ecm is where the relay coil is powered from. i'm going to guess the issue is the tcm is fried or theres a blown fuse somewhere or you let the magic smoke out of it,there is the possibility the ecm is kaput too. I have replaced a couple ecm's for no start issues, but with the no prndl display I'm leaning towards an issue with the tcm or a comm issue.

I sure hope it's not the ECM!!! the dang TCM is $700, i'd hate to know what an ECM runs!!!

As I think I said in my original post, I have 12V in to the TCM, but nothing coming out...is it possible the TCM is getting a bad signal (or no signal at all) that's telling it to stop the starting circuit??? or should it just go straight through the TCM??

 

[IdahoRob]

What usually has happened is the ground side of the jumper cables touches the tcm using it's ground, thus burning it up. This is why GM starting putting covers over the tcm.

So if you have a no crank issue after jump starting and think the tcm has been touched, ground the case of the tcm and this will get you up and running. I had a customer use this technique for over a year until he found a used tcm.(thanks Darryl).

I posted this info on another forum a while ago and had a guy call me and said it saved his family vacation.

 

[IdahoRob]

The LBZ/LMM will not start without a tcm signal. They will stay running if the tcm is removed or fried after engine is already running.

 

[jrodd]

What usually has happened is the ground side of the jumper cables touches the tcm using it's ground, thus burning it up. This is why GM starting putting covers over the tcm.

So if you have a no crank issue after jump starting and think the tcm has been touched, ground the case of the tcm and this will get you up and running. I had a customer use this technique for over a year until he found a used tcm.(thanks Darryl).

I posted this info on another forum a while ago and had a guy call me and said it saved his family vacation.

Sounds like a great idea!!! so, how can I safely go about grounding the case??

 

[jrodd]

holy crap!!! just pulled the tcm loose from the mounting point, leaned it against the ground next to the B+ terminal and wala!!! it started!!! so, does this mean the ground is fried inside the TCM and I need a new one all together?? and again, how should I go about grounding it somewhat 'permanantly' until I can hunt down a used TCM???

 

[IdahoRob]

Yes, ground inside is gone. Need to clamp or solder a wire to the case to operate the truck. Glad it worked out.

 

[jrodd]

got it!!! soldered a wire to one of the large pegs on the case and found a nearby chasis ground...good to go...now i just need to try to find a used TCM!!!

Thanks for the help guys!!!

 

[Bryce418]

Glad to hear you got a band aid fix for now.

One thing to be thoughtful of is a gm gen 4 Allison and Allison gen 4 tcm somehow different. I was trying recently to help out some of the guys at a local Allison dealer program a tcm and I wasn't able to program the tcm from Allison despite being the same part number. The gm part programmed first try.

 

[x MadMAX DIESEL]

For all you guys out there, jump starting is a thing of the past. Don't do it unless you are ready to pay a price.

There was a thread over on DF about this. Someone showed the TSB about it no start after jump start. The problem was I think being no sheild on the TCM people were acidently grounding it out with a jumper cable. That was the only way possible that it could have shorted out (atleast what GM thinks) so Its more a be careful thing, than dont jump start atall.