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DTC U1000: Class 2 Serial Data Link Malfunction

WARNING: This page is about a different car, the 1999 Pontiac Grand Am and 1999 Oldsmobile Alero. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: If circuit is shorted to ground, fuse will blow. Check fuse before performing diagnostics.
  1. Connect scan tool to Data Link Connector (DLC) and check for loss of communication DTCs in the range of U1001-U1199. If any DTCs within this range exist, go to appropriate DTC diagnosis and repair procedure. See BCM DTC DEFINITIONS  table under SELF-DIAGNOSTIC SYSTEM. If no additional DTCs are set, go to next step.
  2. Turn ignition on. Using scan tool, communicate with each module along the class 2 serial data line. Compare modules communicating with scan tool to actual modules along class 2 line. If any modules are not communicating, go to next step. If all modules communicate, go to step  11 .
  3. Check power circuit of non-communicating module for open or short to ground conditions. If faulty circuit is found, repair as necessary and go to step  10 . If circuits are okay, go to next step.
  4. Turn ignition off. Check ground circuit of non-communicating module for open condition. If faulty circuit is found, repair as necessary and go to step  10 . If circuits are okay, go to next step.
  5. Check for poor connections at power, ground and class 2 circuits at non-communicating module connector. If faulty connection is found, repair as necessary and go to step  7 . If connections are okay, go to next step.
  6. Replace non-communicating module. See appropriate removal and installation procedure for module. After repairs, go to step  10 .
  7. Connect scan tool to DLC. Turn ignition on. Select DISPLAY DTCs function for non-communicating module. If any DTCs are present that do not start with "U", go to appropriate DTC diagnosis and repair procedure. See BCM DTC DEFINITIONS  table under SELF-DIAGNOSTIC SYSTEM. If DTCs are not present that do not start with "U", go to next step.
  8. Using scan tool, clear DTCs. Go to step  10 .
  9. Using scan tool, select DISPLAY DTCs function for non-communicating module that had DTC U1000 or U1255 set as current. If any DTCs are present that do not start with "U", go to appropriate DTC diagnosis and repair procedure. If DTCs are not present that do not start with "U", go to next step.
  10. Using scan tool, clear DTCs. Go to DATA LINK CONNECTIONS DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS.
  11. If any additional DTCs are set for non-communicating module that had DTC U1000 or U1255, go to appropriate DTC diagnosis and repair procedure for appropriate module. If no additional DTCs are set, go to next step.
  12. Connect scan tool to DLC. Turn ignition on and clear DTCs. Turn ignition off for a minimum of 5 seconds, and then turn ignition back on. Display DTCs with scan tool. If DTC U1000 or U1255 set as current, go to next step. If DTC do not set, go to DATA LINK CONNECTIONS DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS.
  13. Replace non-communicating module that had DTC U1000 or U1255 set as current. After repairs, go to DATA LINK CONNECTIONS DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS.
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