Receive your CBT yet Ben?
Yeah I got it, played around with an LBZ ECM on the bench and it works really well. No more buffer-full errors and the software the comes with it is great...makes it much easier to filter by message ID, etc.
I've been reading up on GMLAN, there is 2 different bus layouts in a LMM truck. Here is a few notes to get you started. According to the 08 LMM schematics, you can access both the high speed and low speed bus directly from the DLC plug. Low speeds a single wire as noted below. The CBT can also connect to it, with some modified code listed on their forum.
Yeah, 2007.5, Low speed GMLAN (single wire CAN) replaced Class 2 for entertainment/comfort/interior stuff. Its faster than Class 2 (10.4k) but slower than HS GMLAN, LS GMLAN works at 33.3(3333333k, divisor/factor of slowed down 500k high speed GMLAN/CAN).
I was looking around at how to make the CBT work with LS GMLAN...at first I was going to take apart the CBT and remove one of the high-speed CAN transceivers and fab in a SWCAN transceiver chip...but I wasnt sure if the CBT would autodetect 33.33k, because its not listed in the drop down menu. I did some quick looking around but wasnt able to find out if anyone had successfully done any mods to get it to force 33.33k SWCAN. It looks like its all potted inside, so there goes that idea of taking it apart. But maybe with some filtering or passive components I can make it work by tying the "CAN LO" wire of one of the CAN channels to ground, and then tie the CAN-HI wire to the LS GMLAN wire at the OBD port (pin 2).
I dont have a full 2007.5+ truck here to mess with, but I have an instrument cluster and BCM from a GMT-900 that I could play with.
More detailed info about connecting to GMLAN on the MP3 car site at:
http://www.mp3car.com/engine-manage...ics-etc/139533-low-speed-gmlan-interface.html
Most stuff anyone would be looking to tap into, such as steering wheel buttons, OnStar, security, DIC, and IPC all talk over the low speed bus.. The ECM, TCM, and BCM talk on the high speed bus at 500k.
Yeah, the only stuff on HS GMLAN/2-wire-CAN is the ECM, TCM, GPCM (glow plug), TBC (trailer brake control), EBCM (ABS module), VCIM (onstar), TCSM (transfer case shift module), and BCM. All of those above listed modules communicate ONLY on HS GMLAN.
And then there is a secondary isolated HS GMLAN bus for 2009+ Duramax trucks that have stability control, for the steering wheel position sensor and yaw rate/lat-accel sensor...but that is just between the EBCM, yaw sensor, and steering angle sensor.....that bus is not available at the OBD port or for scan tool usage. The EBCM acts as the gateway for that.
Everything else is on LS GMLAN. The BCM is the only module that communicates on both HS and LS GMLAN, and it is the gateway, as you said. The VCIM might communicate on both too, Ill have to check the schematics. But the BCM is the gateway.
Instrument cluster is LS GMLAN only; BCM receives gauges/warning light info from the ECM, TCM, EBCM, etc via HS GMLAN messages, translates them to LS GMLAN messages, and forwards them to the cluster and anything else on the LS-only bus that needs it (theft deterrent module/immobilizer, door locks, etc)
Im actually more interested in the low-speed GMLAN messages; for sending text to the cluster, spoofing the theft deterrent module (no im not a car thief, its for 2011+ LML standalone applications because no one has figured out how to fully disable the starter relay diagnostic and immobilizer in the LML ECM, so its pretty much impossible to do a standalone LML, unless you swap pretty much everything (BCM, TDM, ignition switch, etc) into the new vehicle.
Also, to keep tap-shift and cruise control functional on 2007.5+ standalone swaps.
If you have links to info of how people have made their CBT work on LS GMLAN, that would be great!
Ben
