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DTC U1000 & U1255: Class 2 Communication Malfunction: Testing

WARNING: This page is about a different car, the 2000 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  1. If any DTCs between U1001-U1254 are set as history, these DTCs must be repaired first. Go to DTC U1001-U1254: LOSS OF COMMUNICATION WITH XXX . 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). Turn ignition on. Using scan tool, attempt to establish communication with all systems connected to data line (i.e., PCM, BCM, RFA). If scan tool communicates with all systems, go to step  13. If scan tool does not communicate with any systems, go to next step.
  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. Disconnect star connectors No. 1 and No. 2. See COMPONENT LOCATIONS . Ensure bus bar is properly inserted. Check for poor connections. If connections are okay, go to next step. If faulty connection is found, repair as necessary and go to step  9.
  6. Check for open in serial data line for module or system not communicating. See DATA LINK CONNECTORS 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.
  7. 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  9.
  8. Replace module not communicating. After repairs, go to step  11.
  9. Turn ignition on. Reconnect all disconnect components and/or connectors. 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 diagnostic system check in appropriate article for module or system not communicating.
  10. Use scan tool to clear all DTCs. Go to next step.
  11. 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, go to diagnostic system check in appropriate article for module or system not communicating.
  12. Use scan tool to clear all DTCs. Test is complete.
  13. 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, go to diagnostic system check in appropriate article for module or system not communicating.
  14. Turn ignition off. Ensure scan tool is connected to DLC. 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 .
  15. Replace module that set DTCs U1000 or U1255 as current. Recheck system operation.
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