Diagnostic Aids
WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
When a malfunction occurs while modules are communicating, a Lost Communication DTC is set as a current DTC. When the ignition is turned OFF, the current Lost Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so DTC U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only DTC U1000 or U1255 is set.