Test Description

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

1) - A DTC U1001 - U1254 "Lost Communications with XXX" with a history status may indicate the cause of U1000 or U1255.
2) - The modules not communicating are the likely cause of U1000 or U1255. The modules that are available on the class 2 serial data circuit are listed in the Circuit Description.
7) - The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001 - U1254 "Lost Communications with XXX" for those modules that it was monitoring.
9) - The modules which can communicate indicate the module which cannot communicate. You must clear the serial data communication DTCs from these modules to avoid future misdiagnosis.
12) - If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
14) - The module which set U1000 or U1255 is the likely cause of the malfunction.

Fig 1: DTC U1000 & U1255 Diagnosis (Steps 1-5)

Courtesy of GENERAL MOTORS CORP.

Fig 2: DTC U1000 & U1255 Diagnosis (Steps 6-12)

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Fig 3: DTC U1000 & U1255 Diagnosis (Steps 13-14)

Courtesy of GENERAL MOTORS CORP.