Diagnostic Aids

The EL-51578 MOST Bus Diagnostic Tool Kit when utilized will cause false GMLAN DTC's to be set as a result, along with loss of bypassed MOST device infotainment functionality. These DTC's and missing functionality should be ignored unless the system is completely assembled and a DTC or symptom is present during the repair verification steps.
To troubleshoot the intermittent condition, manipulate or wiggle MOST wiring harness and observe the Radio's DTC U0028 status and the Radio scan tool Number of MOST Communication Breaks parameter value.
If the issue still exists after performing all verification and test steps in this diagnostic procedure, bypass each MOST device individually on the MOST bus (except the Radio) while monitoring DTC U0028 status. If DTC U0028 remains current after each MOST device has been bypassed, disconnect the Radio MOST harness connector. The entire MOST ring can now be tested with all MOST devices (except the Radio) bypassed to determine if any circuit faults exist.
The Radio's DTC U0028 will be set current with all MOST devices bypassed.