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DTC U1255: Generic Loss Of Class 2 Devices: Testing

NOTE: To identify wire colors and components on class 2 serial data line, see appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS.
  1. Connect scan tool to DLC and check for loss of communication DTCs in the range of U1001-U1199. If any DTCs within this range exist, go to DTC U1128: LOSS OF SERIAL COMMUNICATIONS - IRC  . If no additional DTCs are set, go to next step.
  2. Turn ignition on. Use scan tool to 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  9 . 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  9 . 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  9 .
  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. Use scan tool to clear DTCs. Go to step  2 .
  9. Use scan tool to 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. See BCM DTC DEFINITIONS  table under SELF-DIAGNOSTIC SYSTEM. If DTCs are not present that do not start with "U", go to next step.
  10. Using scan tool, clear DTCs. System is okay.
  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 sets as current, go to next step. If DTC does not set, system is okay.
  13. Replace non-communicating module that had DTC U1000 or U1255 set as current.
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