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DTC U1000 & DTC U1255: Class 2 Communication Malfunction: Testing

NOTE: To identify wire colors and modules on serial data links, see appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS.
  1. Ensure battery condition, cold cranking amperage and reserve capacity meet specifications. Replace as necessary. Install scan tool to Data Link Connector (DLC). If DTCs in range of U1001-U1254 are displayed, go to DTC U1001-U1254: LOSS OF XXX COMMUNICATIONS  . If DTCs in range of U1001-U1254 are not displayed, go to next step.
  2. Turn ignition on, engine off. Try to establish scan tool communication with each module on the class 2 device. (On Tech II scan tools, CLASS 2 MESSAGE MONITOR feature). Record all modules communicating on class 2 device. Compare list of modules communicating with scan tool to list of modules connected on serial data links. See appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS. If there are any modules 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 device for opens or shorts to ground. See appropriate wiring diagram in POWER DISTRIBUTION article in WIRING DIAGRAMS. Repair identified circuit(s) as necessary. After repair, go to step  9 . If no problem was found or condition still exists, go to next step.
  4. Turn ignition off. Test ground circuit for module(s) not communicating on class 2 device for opens. See appropriate wiring diagram in GROUND DISTRIBUTION article in WIRING DIAGRAMS. Repair identified circuit(s) as necessary. After repair, go to step  9 . If no problem was found or condition still exists, go to next step.
  5. Disconnect 12-pin splice pack SP205. See Figure . Inspect connector for poor connections. See WIRING DIAGRAMS  . Repair connector as required. After repair, go to step  9 . If no problem was found or condition still exists, go to next step.
  6. Test class 2 serial data circuit for module(s) not communicating on class 2 device for opens. See WIRING DIAGRAMS  . Repair identified circuit(s) as necessary. After repair, go to step  9 . If no problem was found or condition still exists, go to next step.
  7. Test for poor connections at battery feed, ignition feed, ground and class 2 serial data circuits for module(s) not communicating on class 2 device. See WIRING DIAGRAMS  . Repair identified circuit(s) as necessary. After repair, go to step  9 . If no problem was found or condition still exists, go to next step.
  8. Replace module(s) not communicating on class 2 device. See REMOVAL & INSTALLATION  . After repair, go to step  11 .
  9. Turn ignition off. Install scan tool. Turn ignition on. Using scan tool, select display DTCs for module(s) not communicating on class 2 device. If scan tool displays any DTC not beginning with a "U", perform diagnostic system check for applicable system. See BODY CONTROL MODULE (BCM) DTC DEFINITIONS  table. If scan tool does display any DTC beginning with "U", go to next step.
  10. Using scan tool. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. After clearing DTCs, go to next step.
  11. Using scan tool, select display DTCs for module(s) that had U1000 set as a current DTC. If scan tool displays DTCs not beginning with a "U", perform diagnostic system check for applicable system. See BODY CONTROL MODULE (BCM) DTC DEFINITIONS  table. If scan tool displays any DTC beginning with "U", go to next step.
  12. Using scan tool. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. After clearing DTCs, system is okay.
  13. If any other DTCs are recorded for module(s) that set DTC U1000, perform diagnostic system check for applicable system. See BODY CONTROL MODULE (BCM) DTC DEFINITIONS  table. If no other DTCs are recorded for module(s) that set DTC U1000, go to next step.
  14. Turn ignition off. Connect scan tool. Using scan tool, clear DTCs. Turn ignition off for at least 5 seconds. Turn ignition on. Select display DTCs. See BODY CONTROL MODULE (BCM) DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. If DTC U1000 is present as a current code, go to next step. If DTC U1000 is not present as a current code, go to DIAGNOSTIC AIDS  .
  15. Replace module(s) that had DTC U1000 set as a current DTC. See REMOVAL & INSTALLATION  . Test is complete.
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