Test Description

The numbers below refer to the step numbers on the diagnostic table. See Fig 1 and Fig 2 .

1. 1
   
   A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
2. 2
   
   The modules which is not communicating is the likely cause of U1000 or U1255 being set. The following modules communicate on the class 2 serial data circuit:
   • The electronic climate control module (ECCM)
   • The transfer case shift control module (TCSCM)
   • The electronic brake control module (EBCM)
   • The powertrain control module (PCM)
   • The vehicle interface unit (VIU)
   • The body control module (BCM)
   • The instrument panel cluster (IPC)
   • The driver information center (DIC)
   • The memory seat module (MSM)
   • The 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. 10
   
   The modules which can communicate indicate the module which cannot communicate. You must clear 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 Diagnostic Table (Steps 1-7)
Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC U1000 & U1255 Diagnostic Table (Steps 8-15)
Courtesy of GENERAL MOTORS CORP.