I'm wondering if the hardware portion of the interface (which I guess is the MPVI) follows the SAE J-2534 standard and allows passthrough mode.
My first goal would be just to listen on the CAN bus or GMLAN bus and see what's going on.
Then, if I was feeling particularly manly, I'd get a DTC4220A and plug it into my 2010 Range Rover and see if I can find a pulse!
Thanks!
Dave