DTC U1000 & U1255: Class 2 Communication Malfunction: Testing

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.

Connect scan tool. Turn ignition to RUN position. If DTCs U1001-U1254 are not retrieved as history DTCs, go to next step. If DTCs U1001-U1254 are retrieved as history DTCs, go to step 8.
Turn ignition switch to RUN position. Attempt to communicate with all modules on class 2 serial data circuit. Record modules that are communicating on class 2 serial data circuit. If any module does not communicate on class 2 serial data circuit, go to next step. If all modules communicate on class 2 serial data circuit, go to step 12.
Inspect voltage circuits of module that is not communicating for an open or short to ground. See POWER DISTRIBUTION article in WIRING DIAGRAMS. If an open or short to ground is not found, go to next step. If an open or short to ground is found, repair as necessary then go to step 12.
Turn ignition switch to OFF position. Inspect ground circuits of module that is not communicating for an open. See GROUND DISTRIBUTION article in WIRING DIAGRAMS. If an open is not found, go to next step. If an open is found, repair as necessary then go to step 12.
Disconnect splice pack 12-pin connector. Splice pack is located below left side of instrument panel, near Data Link Connector (DLC). See Figure. Inspect splice pack connector for poor or corroded connections. If poor or corroded connections are not found, go to next step. If poor or corroded connections are found, repair as necessary then go to step 12.
Inspect class 2 serial data circuit, voltage circuit and ground circuit of module that is not communicating for poor connections. If no poor connections are found, go to next step. If poor connections are found, repair as necessary then go to step 12.
Replace module that is not communicating on class 2 serial data circuit. Program module, if necessary. See PROGRAMMING . After replacement, go to step 12.
Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel. Turn ignition switch to RUN position. Select DISPLAY DTCs function for suspect module. If scan tool does not display any DTCs which begin with "U", go to next step. If scan tool displays any DTCs which begin with "U", perform TEST B: SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS.
Using scan tool, clear DTCs. When DTCs have been cleared, go to next step.
Using scan tool, select DISPLAY DTCs function for module that set U1000 as a current DTC. If scan tool displays DTCs that do not begin with "U", go to next step. If scan tool displays DTCs that begin with "U", perform appropriate diagnostic system check. See DIAGNOSTIC SYSTEM CHECK table under SELF-DIAGNOSTIC SYSTEM.
Using scan tool, clear DTCs. When DTCs have been cleared, go to next step.
If other DTCs are not set as a current DTC for module that set current DTC U1000, go to next step. If any other DTCs are set as a current DTC for module that set current DTC U1000, perform appropriate diagnostic system check. See DIAGNOSTIC SYSTEM CHECK table under SELF-DIAGNOSTIC SYSTEM.
Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel, to right of steering column. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 5 seconds. Turn ignition switch to RUN position. Using scan tool, select display DTCs functions. If scan tool displays U1000 as a current DTC, go to next step. If scan tool does not display U1000 as a current DTC, see DIAGNOSTIC AIDS .
Replace module that is not communicating. Program module, if necessary. See PROGRAMMING . After replacement, go to next step.