DTC U1000 & U1255: Class 2 Communication Malfunction: Description
WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
Powertrain Control Module (PCM), Electronic Brake Control Module (EBCM), Sensing Diagnostic Module (SDM) and Instrument Panel Cluster (IPC) communicate through a class 2 serial data circuit monitor during normal vehicle operation. When a module receives a message for a critical operating parameter, a module records identification number of module which sent message for State Of Health (SOH) monitoring. When a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, DTC U1000 is set. When one or more critical parameter does not have an identification number associated with it, DTC U1000 will only be reported once.