Diagnostic Aids
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2004 GMC Yukon XL, 2004 GMC Yukon, 2004 Chevrolet Tahoe, 2004 Chevrolet Suburban, and 2004 Chevrolet Avalanche. 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 modules stop communicating 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 U1000 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 is set.