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DTC U1000 & U1255: Class 2 Communication Malfunction: Testing

  1. If any DTCs between U1001-U1254 are set as history, go to BODY CONTROL SYSTEM DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table under SELF-DIAGNOSTIC SYSTEM. If no DTCs between U1001-U1254 are set as history, go to next step.
  2. Turn ignition off. Connect scan tool to Data Link Connector (DLC). See Figure . Turn ignition on. Using scan tool, attempt to establish communication with other systems connected to data line. If Tech 2 is used, select CLASS 2 MESSAGE MONITOR feature. If any module does not communicate with scan tool, go to next step. If scan tool communicates with other systems, go to step  11 .
  3. Check for open or short to ground in battery supply and ignition supply voltage circuit for module or system not communicating. See POWER DISTRIBUTION article in WIRING DIAGRAMS. If circuits are okay, go to next step. If faulty circuit is found, repair as necessary and go to step  9 .
  4. Turn ignition off. Check for open in ground circuit for module or system not communicating. See GROUND DISTRIBUTION article in WIRING DIAGRAMS. If circuits are okay, go to next step. If faulty circuit is found, repair as necessary and go to step  9 .
  5. Check for poor connections at battery supply, ignition supply, ground and serial data line terminals for module or system not communicating. If connections are okay, go to next step. If faulty connection is found, repair as necessary and go to step  7 .
  6. Replace module not communicating. See appropriate procedure under REMOVAL & INSTALLATION  . After repairs, go to step  9 .
  7. Connect scan tool to DLC. Turn ignition on. Display DTCs for module or system not communicating. If no additional DTCs that do not begin with "U" are set, go to next step. If any DTCs that do not begin with "U" are set, go to appropriate diagnostic system check in appropriate article for module or system not communicating.
  8. Use scan tool to clear all DTCs. Go to next step.
  9. Display DTCs for module that set DTC U1000 or U1255. If no additional DTCs that do not begin with "U" are set, go to next step. If any DTCs that do not begin with "U" are set, diagnose set DTCs. See BODY CONTROL SYSTEM DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table under SELF-DIAGNOSTIC SYSTEM. If referred from another article, return to that article and diagnose DTCs.
  10. Use scan tool to clear all DTCs. Test is complete.
  11. If no additional DTCs are set for module that has DTC U1000 or U1255 set as current, go to next step. If any additional DTCs are set for module that has DTC U1000 or U1255 set as current, diagnose set DTCs. See BODY CONTROL SYSTEM DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table under SELF-DIAGNOSTIC SYSTEM. If referred from another article, return to that article and diagnose DTCs.
  12. Turn ignition off. Install scan tool. Turn ignition on. Clear all DTCs using scan tool. Turn ignition off for a minimum of 5 seconds. Turn ignition on. Check for DTCs. If DTCs U1000 or U1255 are set as current, go to next step. If DTCs U1000 or U1255 are not set as current, go to DIAGNOSTIC AIDS  .
  13. Replace module that set DTCs U1000 or U1255 as current. See appropriate procedure under REMOVAL & INSTALLATION  . Recheck system operation.
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