DTC U1000 Or U1255: Class 2 Communication Malfunction: Description

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2002 GMC Savana, 2002 Chevrolet Chevy Express, 2001 GMC Savana Special, 2001 GMC Savana Camper Special, and 2001 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.

Modules connected to class 2 serial data line monitor serial data communications during normal vehicle operation. Operating information and commands are exchanged between modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State Of Health (SOH) monitoring.

When a critical operating parameter is not received by a module, the module uses a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within about 5 seconds of beginning communication, DTC U1000 or U1255 is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once.