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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 21 (BODY CONTROL MODULES)DIAGNOSTIC TESTSDTC U1001-U1254: LOSS OF XXX COMMUNICATIONSTESTING
1999 GMC Forward Control 5.7 R, Automatic

DTC U1001-U1254: Loss Of XXX Communications: Testing

1999 GMC Forward Control 5.7 R, AutomaticSECTION 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. 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 open or short to ground is found, go to next step. If open or short to ground is found, repair as necessary and go to step  9.
  2. 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 open is found, go to next step. If open is found, repair as necessary and go to step  9.
  3. Disconnect splice pack SP205 connectors. Splice pack SP205 is located behind DLC. See Figure. Check splice pack SP205 connectors for poor connections. If no poor connections are found, go to next step. If poor connections are found, repair as necessary and go to step  7.
  4. 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  7.
  5. 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 7.
  6. Replace module(s) not communicating on class 2 serial data link. See appropriate procedure under REMOVAL & INSTALLATION . After repair, go to step  9.
  7. 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.
  8. Using scan tool, clear DTCs. After clearing DTCs, go to next step.
  9. 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 diagnostic system check for applicable system. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  under SELF-DIAGNOSTIC SYSTEM. Repair as necessary.
  10. Using scan tool, clear DTCs. Continue diagnosing and/or clearing DTCs until all modules have been diagnosed and/or all DTCs are cleared. After repair, system is okay.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
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