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DTC U1001 & U1254: Loss Of XXX Communications: Testing

WARNING: This page is about a different car, the 2001 GMC Safari and 2001 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check for open or short to ground in battery supply voltage circuit to module identified as not communicating. See POWER DISTRIBUTION article in WIRING DIAGRAMS. If battery supply voltage exists, go to next step. If battery supply voltage does not exist, repair as necessary and go to step  7 .
  2. Turn ignition switch to OFF position. Check for open in ground circuit to module identified as not communicating. See GROUND DISTRIBUTION article in WIRING DIAGRAMS. If ground circuit is okay, go to next step. If ground circuit is open, repair as necessary and go to step  7 .
  3. Disconnect Natural 12-pin splice pack SP261 connector, located below instrument panel fuse block, taped to body harness. See Figure . Check for poor contact or damage. If no problem is found, go to next step. If problem is found, repair as necessary. After repair, go to step  7 .
  4. Check for open in class 2 serial data line for module that is not communicating. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. If circuit is okay, go to next step. If faulty circuit is found and repaired, go to step  7 .
  5. Check for poor connections at battery supply, ground and serial data line terminals for module identified as not communicating. If connections are okay, go to next step. If faulty connections are found, repair as necessary and go to step  7 .
  6. Replace module that is not communicating. See appropriate removal and installation procedure in appropriate article. Go to next step.
  7. Connect scan tool to DLC. Turn ignition switch to RUN position. Display DTCs for module identified as not communicating. If scan tool displays any DTCs that do not begin with a "U", perform appropriate diagnostic system check. See appropriate diagnostic system check in appropriate article for module identified as not communicating. If scan tool does not display any DTCs that do not begin with a "U", go to next step.
  8. Use scan tool to clear DTCs. Go to next step.
  9. Display DTCs for module that had a loss of communication DTC. If scan tool displays any DTCs that do not begin with a "U", perform appropriate diagnostic system check. See appropriate diagnostic system check in appropriate article for module that had a loss of communication DTC. If scan tool does not display any DTCs that do not begin with a "U", go to next step.
  10. Use scan tool to clear DTCs. Continue diagnosing or clearing DTCs until all modules with stored DTCs are repaired. Test is complete.
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