DTC U1000 & U1255: Class 2 Communication Malfunction: Description

WARNING: This page is about a different car, the 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, 2001 Chevrolet Monte Carlo, and 2001 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

Modules connected to class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among modules. When a module receives a message for a critical operating parameter, module records identification number of module which sent message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that module use a default value for that parameter. When a module does not associate an identification number with at least 1 critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. When more than one critical parameter does not have an identification number associated with it, DTC will only be reported once.

DTC U1000 or U1255 is set when, at least one critical operating parameter has not been associated with an identification number within about 5 seconds after beginning serial data communication. When U1000 or U1255 is set, module uses a default value for missing parameter.

Current DTC U1000 or U1255 clears and becomes a history DTC when malfunction is no longer present. History DTC U1000 or U1255 clears when module ignition cycle counter reaches reset threshold, without a repeat of malfunction.