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Scan Tool Does Not Communicate With Class 2 Serial Data Line

WARNING: This page is about a different car, the 1999 GMC Sierra and 1999 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: To identify wire colors and modules on Class 2 serial data line, see appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS.
  1. Turn ignition off. Connect scan tool to Data Link Connector (DLC). Turn ignition on, with engine off. If scan tool powers up, go to step  9 . If scan tool does not power up, go to next step.
  2. Disconnect scan tool. Check for proper connection of scan tool to DLC terminals No. 4 (Black wire) and No. 16 (Orange wire). If connections are okay, go to next step. If connections are faulty, go to step  5 .
  3. Using DVOM, measure voltage between ground and DLC terminal No. 16 (Orange wire). If battery voltage exists, go to next step. If battery voltage does not exist, go to step  7 .
  4. Using DVOM, measure resistance between ground and DLC terminal No. 4 (Black wire). If resistance is 0-5 ohms, go to step  6 . If resistance is not 0-5 ohms, go to step  8 .
  5. Repair connections as necessary. After repair, recheck system operation.
  6. Check scan tool for malfunction. Refer to scan tool instruction manual. Use a known-good scan tool and go to step  1 .
  7. Repair open in Orange wire between DLC and underhood bussed electrical center (UBEC). See DATA LINK CONNECTOR article in WIRING DIAGRAMS. After repairs, recheck system operation.
  8. Repair open in Black wire between DLC and ground connection G203. See COMPONENT LOCATIONS  and WIRING DIAGRAMS  . After repairs, recheck system operation.
  9. Turn ignition switch to RUN position. Using a scan tool, attempt to establish communication with each module on the Class 2 data link. If any modules are communicating, go to next step. If no modules are communicating, go to step  13 .
  10. If DTCs U1000 or U1xxx (Lost Communication With xxx Module) are set in modules which communicated, go to next step. If DTCs U1000 or U1xxx (Lost Communication With xxx Module) are not set in modules which communicated, go to step  12 .
  11. Diagnose Class 2 communication malfunction for module that is communicating using appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS. After repair, recheck system operation.
  12. Diagnose Class 2 loss of communication for module that is not communicating using appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS. After repair, recheck system operation. After repair, recheck system operation.
  13. Turn ignition off. Check scan tool for proper connection at DLC terminal No. 5 (Black/White wire). If connection is okay, go to next step. If connection is faulty, go to step  5 .
  14. Using DVOM, measure resistance between ground and DLC terminal No. 5 (Black/White wire). If resistance is 0-5 ohms, go to next step. If resistance is not 0-5 ohms, go to step  30 .
  15. Check scan tool for proper connection at DLC terminal No. 2 (Purple wire). If connection is okay, go to next step. If connection is faulty, go to step  5 .
  16. Disconnect splice pack SP205. See COMPONENT LOCATIONS  . Check for proper connection of Class 2 serial data circuit at terminal "A" (Purple wire) of splice pack. If connection is okay, go to next step. If connection is faulty, go to step  5 .
  17. Using DVOM, measure resistance of Purple wire between DLC terminal No. 2 and splice pack SP205 terminal "A". If resistance is 0-5 ohms, go to next step. If resistance is not 0-5 ohms, go to step  29 .
  18. Using DVOM, measure resistance between DLC terminals No. 2 (Purple wire) and No. 4 (Black wire). If resistance is infinite, go to next step. If resistance is not infinite, go to step  28 .
  19. Turn ignition on. Using DVOM, measure voltage between DLC terminals No. 2 (Purple wire) and No. 4 (Black wire). If reading is 0-1 volt, go to next step. If reading is not 0-1 volt, go to step  27 .
  20. Turn ignition off. Using Terminal Adapter Kit (J35616-A), connect appropriate terminal adapter to splice pack SP205. Connect a jumper wire between splice pack SP205 terminal "A" (Purple wire) and to terminal connected to affected module in splice pack SP205. Turn ignition on. Using scan tool, attempt to establish communication with module which is jumpered to DLC. If communication can be established, go to next step. If communication cannot be established, go to step  22 .
  21. Repeat step  20 for each module on Class 2 serial data link. If communication can be established for each module, go to step  31 . If communication cannot be established for each module, go to next step.
  22. Turn ignition off. Disconnect module which does not communicate. Check resistance from splice pack SP205 terminal to Class 2 serial data circuit for disconnected module to ground. See WIRING DIAGRAMS  . If resistance is infinite, go to next step. If resistance is not infinite, go to step  28 .
  23. Turn ignition on. Using DVOM, measure voltage from class 2 serial data circuit of disconnected module to ground. If reading is 0-1 volt, go to next step. If reading is not 0-1 volt, go to step  27 .
  24. Turn ignition off. Inspect connector of disconnected module in area of Class 2 serial data circuit for backed out terminals, causing a short to ground or voltage. If all terminals are properly locked into connector body, go to next step. If terminals are not properly locked into connector body, go to step  5 .
  25. Replace module that does not communicate. Reconnect splice pack SP205. Reconnect all modules on Class 2 serial data link. Turn ignition on. Using scan tool, attempt to establish communication with module that was replaced. If communication can be established, go to step  31 . If communication cannot be established, go to next step.
  26. Replace Class 2 serial data circuit wire between splice pack SP205 and module that does not communicate. After repairs, go to step  31 .
  27. Turn ignition off. Repair short to voltage in Class 2 serial data circuit. See WIRING DIAGRAMS  . After repairs, go to step  31 .
  28. Repair short to ground in Class 2 serial data circuit. See WIRING DIAGRAMS  . After repair, go to step  31 .
  29. Repair open in Class 2 serial data circuit. See WIRING DIAGRAMS  . After repairs, recheck system operation.
  30. Repair open in Black/White wire between DLC terminal No. 5 and ground connection G103. See WIRING DIAGRAMS  . After repairs, recheck system operation.
  31. Reconnect splice pack SP205 and all modules on Class 2 serial data link. Turn ignition on. Wait 10 seconds. Check for DTCs in each module on Class 2 serial data link. If any current "U" codes/DTCs exist, go to step  33 . If no current "U" codes/DTCs exist, go to next step.
  32. If other DTCs are set (not "U" code), go to next step. If no other codes/DTCs are set, go to step  34 .
  33. Diagnose DTC(s) set. Perform appropriate test under DIAGNOSTIC TESTS. Go to BCM DTC DEFINITIONS  table under SELF-DIAGNOSTIC SYSTEM. After diagnosing DTC(s), go to next step.
  34. If all DTCs have been diagnosed, go to next step. If not all DTCs have been diagnosed, go to step  33 .
  35. Clear all DTCs. After clearing DTCs, recheck system operation.
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