Diagnostic Aids
WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
If a malfunction such as an open fuse to a module occurs while serial data communication is active, a Lost Communication DTC for the specific module is set as a current DTC in other modules. When all serial data communication becomes inactive, the current Lost Communication DTC is cleared, but the history DTC remains. When serial data communication resumes, the module with the open fuse will not be learned by the other modules, so DTC U1000 or U1255 is set as current by the other modules.
In the event of a malfunction occurrence while serial data communication is inactive, DTC U1000 or U1255 is set without a loss of communication DTC for the specific module.