Allison 6sp: A50 TCM in LBZ?

[darkone98]

I have a friend who has accidentally fried his TCM by touching a booster cable to the housing, and he purchased a new one at the local dealership. He was told it did not need a flash. The truck is a 2006 and throws ABS/Brake lights, has no gear indicator, speedometer, and will not shift from 1st gear. My V2 throws p0602 which is the TCM is not programmed. The TCM that was sold to him is an A50, instead of an A40, and is not flash-able. Is a Tech2 able to flash this controller with an LBZ OS? I thought I had read that the A40 ran on class 2 and the A50 on GMLAN low speed, and is therefore incompatible.

 

[THEFERMANATOR]

I thought the new A40 replacement TCM's were A46's. Yes for now you are stuck with GM to flash it.

 

[Cougar281]

I have a friend who has accidentally fried his TCM by touching a booster cable to the housing, and he purchased a new one at the local dealership. He was told it did not need a flash. The truck is a 2006 and throws ABS/Brake lights, has no gear indicator, speedometer, and will not shift from 1st gear. My V2 throws p0602 which is the TCM is not programmed. The TCM that was sold to him is an A50, instead of an A40, and is not flash-able. Is a Tech2 able to flash this controller with an LBZ OS? I thought I had read that the A40 ran on class 2 and the A50 on GMLAN low speed, and is therefore incompatible.

The A40 can communicate on Class2 & GMLAN as well as High Speed and Low speed GMLan - it's all in the Calibrations. The A40 is used in the LBZs and LMMs. As far as I know, there is no calibration for an A50 in a LBZ though. A40 & A46 only to the best of my knowledge.

Edit: According to the calibration lookups, yes, only A40 & A46. You'd think they'd make an A50 cal for anything that used an A40 or A46 so they would only need to stock one TCM model for everything from 2006 and up.

 

[darkone98]

Apparently they must have a calibration for LBZ, the A50 is now working in his truck after a reflash from the local dealer.

 

[duratothemax]

Apparently they must have a calibration for LBZ, the A50 is now working in his truck after a reflash from the local dealer.

Wow! Theres something I didnt know. Very strange.... You're sure its an A50 right?

 

[Mike L.]

I ran a A50 in my LML flashed with a '10 Vin #.

 

[Cougar281]

Apparently they must have a calibration for LBZ, the A50 is now working in his truck after a reflash from the local dealer.

Interesting - can you (or he) get the part number off the TCM?

I ran a A50 in my LML flashed with a '10 Vin #.

The difference between that and a LBZ is in the data bus - your LML has the same low speed and high speed GMLAN bus setup as the LMM/LGH trucks and vans. Like the LML/LGH cal for the A50, it is likely an A40/A46 TCM with the same/similar LML/LGH cal would work the same in your LML due to the data bus similarities. My *guess*, though, is that with any LML/LGH cal, be it A40, A46 or A50, the trans would have to run with the same pressure control (or lack therof) as the older Allisons as I doubt any LMM/LGH cal has the ability to control the line pressure the way the LML A50 cal can. The LBZs, however, have the High speed GMLAN for drivetrain module communication and programming, and Class2 for everything else, including DIC information. Technically, a LMM/LML programmed TCM should 'work' in a LBZ as it *should* get all the same info over the HS-GMLAN bus to function and control shifts properly (Although I don't recall if the TCM gets its power on signal from a descrete switched wire or over a data bus), but you would have no DIC info such as gear selector position or manual mode gear indicator. Probably no Trans temp info either.

 

[duratothemax]

Interesting - can you (or he) get the part number off the TCM?



The difference between that and a LBZ is in the data bus - your LML has the same low speed and high speed GMLAN bus setup as the LMM/LGH trucks and vans. The LBZs, however, have the High speed GMLAN for drivetrain module communication and programming, and Class2 for everything else, including DIC information. Technically, a LMM/LML programmed TCM should 'work' in a LBZ as it *should* get all the same info over the HS-GMLAN bus (Although I don't recall if the TCM gets its power up from a descrete switched wire or over a data bus), but you would have no DIC info such as gear selector position or manual mode gear indicator. Probably no Trans temp info either.

So we dont know if the A50 has the ability to speak Class 2 or not.... It appears that GM has made a calibration to enable Class 2 on the A50

OR it COULD be that the A50 does NOT in fact speak Class 2....something is happening where the LBZ ECM recognizes that the A50 TCM has no Class 2 comms enabled, and then the LBZ ECM assumes the role of being a GMLAN <---> Class 2 gateway/translator module.

Because thats how the 06-07 Duramax vans work. Their clusters only speak Class 2. But the T42 TCM that runs the 4L80 in the duramax vans does not speak Class 2. So what the LBZ ECM in the Duramax vans does, is receive PRND321 status, trans temp, etc from the T42 via high speed GMLAN. And then it translates that HS GMLAN message to Class 2, and passes it along to the cluster for PRND321 info, tow/haul requests, etc.

So who knows.

To test that theory, I guess you could dig into the TCM harness, cut/remove the Class 2 wire going to the A50/LBZ TCM, and see if your cluster display and trans temp still works.

If it does, then thats whats happening. The LBZ ECM automatically starts acting like a gateway/translator between the GMLAN-only A50 and the Class2-only GMT-800 cluster/body.

And if the cluster and everything stops working when you cut the Class 2 wire going to the A50 TCM, then we know that GM actually made a special A50 calibration that turns on Class 2 in the A50.

 

[duratothemax]

Im still skeptical. Is he sure that the dealer didnt realize the error, and then swap out the A50 TCM with an A40/A46???

I just looked through a couple VIN's and all of the supported TCM part numbers for LBZ's, and it makes no mention of A50 or an A50 part number cross reference.

Can your buddy get the part number off of the A50 in his truck??

 

[Cougar281]

So we dont know if the A50 has the ability to speak Class 2 or not.... It appears that GM has made a calibration to enable Class 2 on the A50

OR it COULD be that the A50 does NOT in fact speak Class 2....something is happening where the LBZ ECM recognizes that the A50 TCM has no Class 2 comms enabled, and then the LBZ ECM assumes the role of being a GMLAN <---> Class 2 gateway/translator module.

Because thats how the 06-07 Duramax vans work. Their clusters only speak Class 2. But the T42 TCM that runs the 4L80 in the duramax vans does not speak Class 2. So what the LBZ ECM in the Duramax vans does, is receive PRND321 status, trans temp, etc from the T42 via high speed GMLAN. And then it translates that HS GMLAN message to Class 2, and passes it along to the cluster for PRND321 info, tow/haul requests, etc.

So who knows.

To test that theory, I guess you could dig into the TCM harness, cut/remove the Class 2 wire going to the A50/LBZ TCM, and see if your cluster display and trans temp still works.

If it does, then thats whats happening. The LBZ ECM automatically starts acting like a gateway/translator between the GMLAN-only A50 and the Class2-only GMT-800 cluster/body.

And if the cluster and everything stops working when you cut the Class 2 wire going to the A50 TCM, then we know that GM actually made a special A50 calibration that turns on Class 2 in the A50.

I wouldn't be the slightest bit surprised if the A50 can support Class2 - it's not a GM controller, after all, but an Allison, and the Allison TCMs go in all kinds of applications requiring all kinds of communications protocols, not just GM Trucks - I think it all comes down to the calibration.

Interesting about the T42 in the vans - did not know that. I want to say that I've plugged a LMM programmed A40 into my truck and did not get the cluster indicators. Very possible that the LBZ ECM (or at least the truck calibrations) doesn't have the code to do the translation. I'd program one of my spare A40s with a LMM cal and test it out, but I'm not spending $55 on a TIS sub just to test it out

Cutting wires to test theories isn't something everyone would do. Just crazy people like us :screwy:

Im still skeptical. Is he sure that the dealer didnt realize the error, and then swap out the A50 TCM with an A40/A46???

I just looked through a couple VIN's and all of the supported TCM part numbers for LBZ's, and it makes no mention of A50 or an A50 part number cross reference.

Can your buddy get the part number off of the A50 in his truck??

I looked it up too - the highest hardware part number listed is a 25982143, which is an A46. The A50's seem to all start with 295.

 

[darkone98]

I will double check and get the part number when I see him next, but I know for a fact it was read as an A50 when I attempted to read it with a V2.

 

[darkone98]

Here is the TCM that is in it, hope this helps. Unfortunately I did not have my V2 with me to read the file.

 

[Cougar281]

Here is the TCM that is in it, hope this helps. Unfortunately I did not have my V2 with me to read the file.
View attachment 34828

According to TIS, the 24256864 hardware is an A46.