Test Description

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

1. A DTC U1001 - U1254 Loss of XXX Communication with a history status may indicate the cause of U1000 or U1255.
2. The modules not communicating is the likely cause of U1000 or U1255. The following modules are available on the class 2 serial data circuit.
   • Inflatable restraint sensing and diagnostic module (SDM)
   • Powertrain control module (PCM)
   • Theft deterrent control module
   • Vehicle interface unit (VIU)
3. The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001 - U1254 Loss of XXX Communication for those modules that it was monitoring.
4. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
5. If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
6. The module which set U1000 or U1255 is the likely cause of the malfunction.

Fig 1: DTC U1000 And U1255 - Diagnostic Table (1 Of 2)

Courtesy of GENERAL MOTORS CORP.

Fig 2: DTC U1000 And U1255 - Diagnostic Table (2 Of 2)

Courtesy of GENERAL MOTORS CORP.