Scan Tool Does Not Communicate with High Speed GMLAN Device: Notes

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications on the high speed GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition a DTC U0001, U2100 or U2104 will be set. Generally these DTCs can be retrieved as history only, with the exception of body control module (BCM) that can set DTC U2100 as current, because it communicates with the scan tool on class 2.