Hmm. Do you need specific voltages to shift the t case? I'm wondering if you could bypass the whole can-bus ECM issue and just use the push buttons on stand alone wiring.
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Hope this helps, this was the in depth response i got when i failed to believe it couldn't be done.
Plagiarized from another forum:
I dont think everyone realizes that the 2003-2006 GMT-800s have just as much "data" going through them and just as many data-controlled modules as the 2008+ new body style trucks. "CAN bus" doesnt mean "oh it has computer data in it". There are DOZENS of different styles/types/protocols of databus's. Everyone thinks that there is only one kind of databus "CAN bus", and vehicles either "have CAN, or no data network at all".
There is so much misinformation out there about the databusses on the GM trucks/SUV's it makes my head hurt.
The Duramax's have had CAN since the beginning, I dont think everyone understands that either. Because they all say "OH the duramax's went CAN in 2006!" No they didnt. They went GMLAN in 2006. And that GMLAN is for ECM-TCM-GPCM communication ONLY. The 2001-2007 trucks did not have any "CAN" or "GMLAN" going through the BODY OR CHASSIS. It was powertrain only.
"CAN" is a general 'style' of databus. Its not a "SPECIFIC protocol". There are many different forms of CAN. Just like every person on Earth is a human being...but there are white people, black people, hispanic, asian, etc... Yeah, we're all humans, but does that mean we can all talk to eachother? No.
1995 (YES, 1995)-2007 GM trucks/SUV's had Class 2 (J-1850) databus running through the body and ECM/TCM. From 1995-2002 it wasnt really "widespread" throughout the body, there were basically only 3-4 modules on it and it wasnt really used that much. Airbag module, BCM (to control central locking etc), ECM, ABS module.
I mean if you want to get really technical, GM trucks have had databusses since TBI came out in what, 1985??? Yep, I can plug my Tech 2 into a 25 year old silverado with an old TBI 350 and read out live data over the bus (spark advance, ignition voltage, rpm, closed/open loop, AC status, etc). OMG CRAZY!!! The refresh rate wasnt fast (160baud IIRC) and there were only 20 or so parameters that could be read (in addition to reading/clearing codes), but hey, it was a databus. Pretty amazing stuff back then. When the new C/K trucks came out in 1988 they had a very basic databus in the body too. It was only used for communication between the climate control module (if you ordered your brand new 1988 truck with the digital climate control, remember that?), radio head unit, and the radio cassette player/EQ (remember how the 88-94 pickup trucks/suburbans had the remote mount EQ and tape player?). It was called the "E&C bus", or Entertainment and Comfort bus.
Fast forward to 2003 when the GM trucks came out with the mid-cycle enhancement and totally new electrical system which took full-advantage of Class 2 and used it for EVERYTHING in the body. The 2003-2007 trucks have well over a dozen different modules talking to eachother over the common Class 2 databus. Everything in the 2003-2012 trucks is controlled by a data signal. When the driver presses the "passenger window up" button on his 2004 Duramax, do you think battery power flows through the switch, through wiring, and then to the passenger side window motor? No. Driver hits the switch, drivers door module sends a data signal requesting "passenger window go up" to the passenger door module, then the passenger door module sends a signal to the window motor to make the window go up.
When you turn the volume up on the radio, do you think the audio outputs on the back of the radio get "louder"? Nope, wrong again. The outputs from the radio are fixed. On the Bose lux vehicles, when you turn the volume knob, the radio sends a data signal to the amplifier, and then the amplifier increases the volume itself, and then sends the amplified signal to the speakers.
Horn? You press the horn button, you arent completing any basic circuit. The horn switch wiring isnt even connected to the horn itself. Well, its connected with a data signal, but not in the normal way horn wiring is controlled.
Interior lights, headlights, etc. All data signals. It saves a huge amount of wiring, and wires dont have to be as heavy too. For example, isnt it ridiculous to have a headlight switch carry the full load of the headlights? You have to send the power all the way from the battery, to the headlight switch, the headlight switch (and high/low beam switch) has to handle ~15amps+, then send the power alll the way back to the headlights. Headlight switch (and high/low beam switch) just sends a data signal to the BCM, and then the BCM sends a signal to the headlight relay under the hood. Same thing with the instrument panel lights dimmer. Theres no rheostat in the headlight switch that then sends out "backlight power" to everything in the truck. The dimmer switch in the headlight switch sends a signal to the BCM, the BCM interprets this, and then the BCM sends a data message to everything in the truck telling it what backlighting brightness to use.
You can see this at night, if you flick the dimmer switch up and down really fast a couple times, you can see how some modules dim at slightly different rates, because some modules take a couple milliseconds longer to receive/process the data signal. Usually the radio is the slowest (most noticeable) to process data signals. Like if you turn the truck off at night, the backlighting on the radio stays on for a good 20 milliseconds after the climate control, instrument cluster, door switch lights have turned off.
So yeah....all the 2003-2007 GM trucks/SUV's most certainly did have a data bus going through them....and it was all the same from 2003-2007. Nothing special or different happened to the body communications/data bus when the LBZ came out.
The 2001-2005 Duramax CAN bus (ECM-TCM-FICM-GPCM only, nothing in the body was CAN) is "SAE J1939". It ran at 250kbps. It was not used for communication with the body, or with the outside world. If you look up the specs for J1939, it is most certainly a variant of CAN bus, so I dont know where people get this BS that "Oh the duramax's went to CAN in 2006 with the LBZ"
In 2006 they switched to a different style of CAN bus, high speed GMLAN. GMLAN and J1939 are relatives, but the messages are different and thats why you cant run a 6-speed TCM with a 2001-2005 duramax ECM. High speed GMLAN runs at 500kbps. The 2006-2007 duramax's still used Class 2 for body communications, JUST THE SAME AS THE 2003-2005 DURAMAX's. So when the LBZ ECM tells the instrument cluster what coolant temperature, trans temp, oil pressure etc is, its still a Class 2 message.
The key difference is that the 06+ duramax's communicate with scan tools (and reflashing) over the high speed GMLAN bus. Whereas the 05 and earlier duramax's communicated with scan tools and did reflashing over Class 2. Thats probably what confuses everyone.
Im probably wasting my breath/fingers writing all this out though because everyone is just going to read the first sentence and then tune-out/skip over to the next post.
If you keep the TCM in place, and run an automatic OS in the ECM, your speedometer, clutch pedal safety switch, and cruise control wont work with no Allison in there. In order to get those working, you have to remove the TCM, rewire the harness, add new wiring, change stuff in the fuse box, and reflash all of the modules with manual-trans operating systems. Because you could never get the push-button transfer case with a manual trans from the factory, there is no such software for the TCSM to work with a manual trans. You are going to have to swap to a manual-shift transfer case if you want low range.
