If you want a deeper discussion of what happens with CANBUS and wire length, see:
http://www.eetimes.com/document.asp?doc_id=1274178
The CAN standard specifies cable with 5ns per meter propagation delay, and a maximum cable length of 40 meters for signaling at 1Mbps.
If a cable stub (unterminated cable) or T-connector is used to tap into the bus line, then the stub distance should not exceed 0.3m at 1Mbit/s rate per DS 102 Version 2.0.
If you want more information on CANBus, see:
http://www.ti.com/lit/an/slla270/slla270.pdf
Realize that GMLAN is developed with CAN technology. GMLAN includes two CAN buses that connect to each other via a “gateway” node. One bus is a high-speed dual-wire CAN, and the other is a lower-speed single wire CAN.
The high-speed dual-wire CAN bus uses a differential signal for noise immunity at relatively high speeds. The bus has a maximum length (from the node at the head of the bus to the node at the tail of the bus) of 30 meters, and the bus can accommodate a maximum of 16 nodes. The bus operates at 500 KBS rather than the maximum CAN specification of one megabit per second since the lower speed allows a longer bus length, reduces radiated emissions, and is sufficient for the high-speed vehicle nodes.
As the lower speed allows longer bus wires, I'm going to assume the above is sufficient.
http://www.public.asu.edu/~pheanis/d...ts/VBI_CAN.pdf
So, the question that you have not answered is: what form of ECU bus are you running and how fast is the vendor using the bus? I covered two most likely options.
Thoughts?
