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Test C: Scan Tool Does Not Communicate With Class 2 Device

NOTE: Class 2 device may also be referred to as class 2 serial data link
NOTE: To identify wire colors and modules on class 2 serial data link, see appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS.
  1. Ensure battery is in good operating condition. Turn ignition off. Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel, to right of steering column. See Figure . Turn ignition on. If scan tool powers up, go to next step. If scan tool does not power up, go to TEST D: SCAN TOOL DOES NOT POWER UP  .
  2. Turn ignition on. Try to establish scan tool communication with each module on class 2 serial data link (on GM Tech 2 scan tools use CLASS 2 MESSAGE MONITOR feature). If communication with any module is established, go to next step. If communication with any module is not established, go to step  7 .
  3. Using scan tool, select DISPLAY DTC function for each module on class 2 serial data link. Record all displayed DTCs, status of displayed DTCs and module that set DTC. If DTCs U1000-U1255 are displayed, go to next step. If DTCs U1000-U1255 are not displayed, go to PRELIMINARY INSPECTION  under TROUBLE SHOOTING.
  4. If DTC U1300, U1301 or U1305 are displayed, go to next step. If DTC U1300, U1301 and U1305 are not displayed, go to step  6 .
  5. Test the class 2 serial data circuit (Purple wire) for an intermittent short to ground or an intermittent short to voltage. If no problem is found, go to next step. If any problem is found, repair as necessary. After repair, go to step  27 .
  6. If DTC U1000 or DTC U1255 is only DTC displayed, go to DTC U1000 & DTC U1255: CLASS 2 COMMUNICATION MALFUNCTION  under DIAGNOSTIC TESTS. If DTC U1000 is not only DTC displayed, go to DTC U1001-U1254: LOSS OF XXX COMMUNICATIONS  under DIAGNOSTIC TESTS.
  7. Turn ignition off. Disconnect scan tool from DLC. Check DLC terminals No. 2 (Purple wire) and No. 5 (Black wire) for poor connections. See Fig 1 . If poor connections are not found, go to next step. If poor connections are found, repair connections as necessary. After repair, appropriate diagnostic system check. See BODY CONTROL SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
    Fig 1: Identifying Data Link Connector Terminals
    G00050869Courtesy of GENERAL MOTORS CORP.
  8. Test Black wire between DLC No. 5 and ground point for an open. Ground point is located below instrument panel, to right of steering column. If an open is not found, go to next step. If an open is found, repair as necessary. After repair, appropriate diagnostic system check. See BODY CONTROL SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  9. Disconnect the rear fuse block connector C1. Disconnect the IP fuse block connector C1. Install scan tool. Turn ignition on. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to next step. If scan tool does not communicate with any module on class 2 serial data circuit, go to step  15 .
  10. Turn ignition off. Disconnect rear fuse block connector C2. Reconnect the rear fuse block connector C1. Turn ignition on. Attempt to communicate with any modules still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to next step. If scan tool does not communicate with any module on class 2 serial data circuit, go to step  25 .
  11. Turn ignition off. Disconnect the IP fuse block connector C4. Reconnect the IP fuse block connector C1. Turn ignition on. Attempt to communicate with any modules still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to next step. If scan tool does not communicate with any module on class 2 serial data circuit, go to step  26 .
  12. Turn ignition off. Reconnect the rear fuse block connector C2. Turn ignition on. Attempt to communicate with any modules still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to next step. If scan tool does not communicate with any module on class 2 serial data circuit, go to step  20 .
  13. Turn ignition off. Disconnect the connector C101. Reconnect the IP fuse block connector C4. Turn ignition on. Attempt to communicate with any modules still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to next step. If scan tool does not communicate with any module on class 2 serial data circuit, go to step  24 .
  14. Turn ignition off. Reconnect the connector C101. Turn ignition on. Attempt to communicate with any modules still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to step  28 . If scan tool does not communicate with any module on class 2 serial data circuit, go to step  20 .
    Fig 2: Identifying Powertrain Control Module Harness Connector C2 Terminals
    G00009284Courtesy of GENERAL MOTORS CORP.
  15. Turn ignition off. Disconnect the connector C200. Turn ignition on. Attempt to communicate with any modules still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to next step. If scan tool does not communicate with any module on class 2 serial data circuit, go to step  20 .
  16. Turn ignition off. Disconnect the DDM. Reconnect the connector C200. Turn ignition on. Attempt to communicate with any modules still connected to the DLC through the class 2 serial data circuit. If scan tool communicates with any module on class 2 serial data circuit, go to next step. If scan tool does not communicate with any module on class 2 serial data circuit, go to step  19 .
    Fig 3: Identifying Electronic Brake Control Module Harness Connector Terminals
    G00032221Courtesy of GENERAL MOTORS CORP.
  17. Turn ignition off. Test the class 2 serial data circuit between DDM and rear fuse block connector C1 for a short to ground or a short to voltage. If open circuit or short to power is not found, go to next step. If open circuit or short to power is found, repair as necessary. After repair, go to step  27 .
  18. Turn ignition off. Replace the DDM. See DOOR MODULE  under REMOVAL & INSTALLATION. After repair, go to step  27 .
    Fig 4: Identifying Sensing & Diagnostic Module Harness Connector Terminals
    G99J00363Courtesy of GENERAL MOTORS CORP.
  19. Test the class 2 serial data circuit between DDM and connector C200 for an open or short to voltage. If open circuit or short to power is not found, go to next step. If open circuit or short to power is found, repair as necessary. After repair, go to step  27 .
  20. Turn ignition off. Disconnect vehicle interface unit connectors. Turn ignition on. Using scan tool, attempt to communicate with vehicle modules still connected. Turn ignition off. Repeat procedure, disconnecting modules one at a time. If communication is possible at any time before disconnecting the last module, stop disconnecting modules and go to next step. If there is no communication after disconnecting all modules, go to step  24 .
    Fig 5: Identifying Instrument Panel Cluster Harness Connector Terminals
    G97E28419Courtesy of GENERAL MOTORS CORP.
  21. Test the class 2 serial data circuit after the last module disconnected for a short to ground or voltage. If no problem is found, go to next step. If any problem is found, repair as necessary. After repair, go to step  27 .
  22. Inspect for poor connections at the harness connector of the last module disconnected. If no problem is found, go to next step. If any problem is found, repair as necessary. After repair, go to step  27 .
    Fig 6: Identifying Heater-A/C Control Module Harness Connector Terminals
    G00032222Courtesy of GENERAL MOTORS CORP.
  23. Replace the last module disconnected. See appropriate removal and installation procedure under REMOVAL & INSTALLATION  . After repair, go to step  27 .
  24. Repair the class 2 serial data circuit(s) and in-line connector(s) between the last module disconnected in the branch being diagnosed. After repair, go to step  27 .
  25. Turn ignition off. Replace the rear fuse block. After repair, go to step  27 .
  26. Turn ignition off. Replace the IP fuse block See appropriate removal and installation procedure under REMOVAL & INSTALLATION  . After repair, go to next step.
    27. NOTE: Scan tool may require a 10 second power-up reset before class 2 serial data link can communicate with scan tool if a short occurred on class 2 serial data link.
  27. Turn ignition off. Disconnect or turn off scan tool. Remove all jumper wires and reconnect all disconnected harness connectors, splice pack SP205 and modules. Turn ignition on. Wait 10 seconds before proceeding. Reinstall or turn scan tool on and select DISPLAY DTC function for each module on class 2 serial data link. Record all displayed DTCs, status of displayed DTCs and module that set DTC. If no DTCs that begin with "U" are displayed as CURRENT, go to next step. If any DTCs that begin with "U" are displayed as CURRENT, go to step  29 .
  28. If any DTCs were recorded that did not begin with "U", go to next step. If DTCs were recorded that begin with "U", go to step  31 .
    29. NOTE: The PCM may have DTC(s) P1602-P1615 or P1626 set. If only P1600 DTC(s) in the range specified along with history U1xxx DTC(s) are set and the vehicle will start and run, repairs are complete.
  29. Diagnose and repair recorded DTCs. Perform appropriate diagnostic procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . After repair, go to next step.
  30. If all DTCs have been diagnosed, go to next step. If all DTCs have not been diagnosed, repeat step  29 .
  31. Using scan tool, clear DTCs. System is okay.
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