Test Description

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 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.
6. 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 (Steps 1 - 5)

Courtesy of GENERAL MOTORS CORP.

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

Courtesy of GENERAL MOTORS CORP.

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

Courtesy of GENERAL MOTORS CORP.