Originally Posted by
DURAtotheMAX
no.....no....
The 8.1 ECM has never had CAN. Duramax's have always had CAN. Yes, even 2001-2005. WHY can everyone not get this through their head. They just changed from J1939 (which is CAN!) to GMLAN (which is also CAN!) in 2006. All this talk of "can bus this" and "can bus that"...when no one even knows what they are talking about. Theres probably a dozen different variations of CAN. Different speeds, different message structure, etc. Everyone just thinks "oh there are two computers talking to eachother, MUST BE 'CANBUS'". And another pet peeve of mine, technically, the data bus is just called CAN, not CAN BUS. Controller Area Network....yeah its a type of dataBUS, but the name for it isnt "CAN bus". Just like my name is BEN...not "BEN HUMAN".... and you call your truck a "chevy silverado" and not a "chevy silverado truck".... but thats semantics, whatever.
Because the 8.1 ECM never supported CAN, GM used 3 discrete torque signal wires (basically just a square wave PWM signal) between the 8.1 ECM and Allison TCM to communicate throttle %, delivered torque, and requested torque for defuel. Because to add CAN controller chips to the 8.1 LS1-b ECM was more expensive than just telling a couple of the general purpose I/O's to read and produce some PWM signals.
2001-2007 8.1 ECM's are all configured the same way...GM made a special calibration for the 06-07 4th gen TCM that used those PWM signal wires, so they wouldnt have to redesign the 8.1 ECM to support GMLAN when the 8.1 was only going to be around for 2 more years anyway.
Its a pain to convert an 01-02 truck to a 6-speed, just because the instrument cluster design is different. You cant just stick an 03-07 cluster in an 01-02 truck. But you can stick an 06-07 cluster in an 03-05 truck. OH BUT WAIT I thought 06+ was "CAN BUS!!?". No...again....no. GMT-800 body was never CAN or GMLAN. Not in 1999, not in 2003, not in 2004, not in 2007. The whole body is Class 2 data bus only. The only "CAN" in an 01-05 Duramax is between ECM and TCM and FICM (and GPCM in LLY)...and the only CAN in an 06-07 Duramax is ECM and TCM and GPCM. The difference is that the 06-07 ECM and TCM did not interface with scan tools via Class 2 like the earlier trucks...they used GMLAN. Thats the only difference. The 06-07 ECM's still talk to the rest of the body with Class 2...its just when you plug your scan tool in to read data and/or reflash, its over GMLAN (CAN) instead of Class 2.
And 99-02 GMT-800's had Class 2...yes...they did. The difference was it wasnt fully integrated. Doors, windows, radio, HVAC, amplifier, lighting, etc was wired the old school way. 03+ the entire electrical system became multiplexed and everything switched over to being controlled by Class 2. The only modules that used Class 2 in 99-02 was the cluster, BCM, transfer case computer, and airbag module. So YES if you wanted to get fancy, you could repin the connector on an 01-02 cluster connector and plug in an 03-07 cluster. But oil pressure gauge wouldnt work unless you used an 03+ operating system in the ECM.
Didnt I already write a novel explaining this a year or so ago? Sometimes I dont even know why I bother.