Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 1)  - A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
2. 2)  - The module which are not communicating will be the likely cause of U1000 or U1255 being set. The following modules communicate on the class 2 serial data circuit:
   • Transfer Case Shift Control Module (TCSCM)
   • Electronic Brake Control Module (EBCM)
   • Powertrain Control Module (PCM)
   • Body Control Module (BCM)
   • Instrument Panel Cluster (IPC)
   • Driver Information Center (DIC)
   • Inflatable Restraint Sensing And Diagnostic Module (SDM)
3. 5)  - The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
4. 6)  - The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
5. 7)  - The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
6. 11)  - The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
7. 13)  - If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
8. 14)  - The module which set U1000 or U1255 is the likely cause of the malfunction.
Fig 1: DTC U1000 & U1255 (Carry Over) (Steps 1-6)
Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC U1000 & U1255 (Carry Over) (Steps 7-15)
Courtesy of GENERAL MOTORS CORP.