Diagnostic Aids
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The modules that communicate on the SAE J1939 CAN system are wired parallel to each other until the respective circuits are spliced together outside of the ECM. An open in the CAN circuits of one module will not affect the other modules. A short to ground or short to voltage affects all modules no matter where the failure occurs.