Test Description

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

1. 1
   
   A module which loses power during an ignition cycle will cause other modules to set Lost Communication DTCs.
2. 2
   
   A module which loses power during an ignition cycle will cause other modules to set Lost Communication DTCs.
3. 3
   
   The malfunction is due to an open in the class 2 serial data circuit or an open in the module.
4. 7
   
   The module which was not communicating may have set Lost Communication DTCs for those modules that it was monitoring.
5. 9
   
   The modules which can communicate indicate the module which cannot communicate. You must clear DTC from these modules to avoid future misdiagnosis.

Fig 1: DTC U1001-U1254 Diagnostic Table (Steps 1-7)

Courtesy of GENERAL MOTORS CORP.

Fig 2: DTC U1001-U1254 Diagnostic Table (Steps 8-10)

Courtesy of GENERAL MOTORS CORP.