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DTC U1000 & U1255: Class 2 Communication Malfunction: Testing

WARNING: This page is about a different car, the 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, 2001 Chevrolet Monte Carlo, and 2001 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Start engine and wait at least 5 seconds. Using scan tool, retrieve DTCs. If history DTCs in range of U1001-U1254 are not set, go to next step. If history DTCs in range of U1001-U1254 are set, go to DTC U1001-U1254: LOSS OF XXX COMMUNICATIONS .
  2. Turn engine off. Turn ignition switch to RUN position. Using CLASS 2 MESSAGE MONITOR of scan tool, try to establish scan tool communication with each module on class 2 serial data link. Record all modules communicating on class 2 serial data link. Compare list of modules communicating with scan tool to list of modules connected on class 2 serial data link. See appropriate DATA LINK CONNECTORS wiring diagram in WIRING DIAGRAMS. If any modules are not communicating, go to next step. If all modules are communicating, go to step  13.
  3. Test battery feed and ignition feed circuits for module(s) not communicating on class 2 serial data link for opens or shorts to ground. See appropriate POWER DISTRIBUTION wiring diagram in WIRING DIAGRAMS. If no opens or shorts to ground are found, go to next step. If opens or shorts to ground are found, repair as necessary and go to step  9.
  4. Turn ignition switch to OFF position. Test ground circuit for module(s) not communicating on class 2 serial data link for opens. See appropriate GROUND DISTRIBUTION wiring diagram in WIRING DIAGRAMS. If no opens are found, go to next step. If opens are found, repair as necessary and go to step  9.
  5. Disconnect splice pack SP205 connector. Splice pack SP205 connector is located behind DLC. See Fig 1. Check splice pack SP205 connector for poor connection. If poor connection is not found, go to next step. If poor connection is found, repair as necessary and go to step  9.
  6. Test class 2 serial data link for module(s) not communicating on class 2 serial data link for opens. See WIRING DIAGRAMS . If no opens are found, go to next step. If opens are found, repair as necessary and go to step  9.
  7. Check for poor connections at battery feed, ignition feed, ground and class 2 serial data link at connectors for module(s) not communicating on class 2 serial data link. See WIRING DIAGRAMS . If no poor connections are found, go to next step. If poor connections are found, repair as necessary and go to step  9.
  8. Replace module(s) not communicating on class 2 serial data link. See appropriate removal and installation procedure under REMOVAL & INSTALLATION . After repair, go to step  11.
  9. Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Turn ignition switch to RUN position. Using scan tool, select DISPLAY DTC function for module(s) not communicating on class 2 serial data link. If scan tool displays any DTC beginning with "U", go to next step. If scan tool displays any DTC not beginning with a "U", perform diagnostic system check for applicable system. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  under SELF-DIAGNOSTIC SYSTEM. Repair as necessary.
  10. Using scan tool, clear DTCs. After clearing DTCs, go to next step.
  11. Using scan tool, select DISPLAY DTC function for module(s) that had DTC U1000 set as current. If scan tool displays any DTC beginning with "U", go to next step. If scan tool displays DTCs not beginning with a "U", perform appropriate diagnostic system check for applicable system. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  under SELF-DIAGNOSTIC SYSTEM. Repair as necessary.
  12. Using scan tool, clear DTCs. After clearing DTCs, system is okay.
  13. If no other DTCs are recorded for module(s) that set DTC U1000, go to next step. If any other DTCs are recorded for module(s) that set DTC U1000, perform diagnostic system check for applicable system. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  under SELF-DIAGNOSTIC SYSTEM. Repair as necessary.
  14. Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Turn ignition switch to RUN position. Using scan tool, clear DTCs. Turn ignition switch to OFF position for at least 5 seconds. Turn ignition switch to RUN position. Using scan tool, select DISPLAY DTC function. If scan tool displays DTC U1000 or DTC U1255 as current, go to next step. If scan tool does not display DTC U1000 or DTC U1255 as a current, go to DIAGNOSTIC AIDS .
  15. Replace module(s) that had DTC U1000 set as a current DTC. See appropriate removal and installation procedure under REMOVAL & INSTALLATION . After repair, system is okay.
Fig 1: Identifying Left Footwell Component Locations
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