1998 GMC EnvoyFACTORY OEM SERVICE PROCEDURE

Diagnostic Procedures

  1. Turn ignition off. Install scan tool. 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 from DLC. Check for proper connection of scan tool to DLC terminals No. 4 (Black wire) and 16 (Orange wire). See WIRING DIAGRAMS  . If connections are okay, go to next step. If connections are faulty, go to step 7).
  3. Using DVOM, check voltage between ground and DLC terminal No. 16 (Orange wire). If voltage reading is about 12 volts, go to next step. If voltage reading is not about 12 volts, go to step 7).
  4. Using DVOM, check 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 repairs, recheck system operation.
  6. Check scan tool for malfunction. Use a known-good scan tool and go to step 1).
  7. Repair open in Orange wire between DLC and instrument panel fuse block. After repairs, recheck system operation.
  8. Repair open in Black wire between DLC and ground connector. After repairs, recheck system operation.
  9. Turn ignition switch to RUN position. Using scan tool, attempt to establish communication with each module on the class 2 data link. See WIRING DIAGRAMS  . If all modules are communicating, go to next step. If not all modules are communicating, go to step 13).
  10. If DTCs U1000 or U1xxx (Lost Communication With xxx Module) is set, go to next step. If other than a "U" type code/DTC(s) is set, go to step 12).
  11. Diagnose affected DTCs. See TBC MODULE DTC DEFINITIONS  table. After diagnosing DTC(s), recheck system operation.
  12. Diagnose affected DTC(s). After diagnosing DTC(s), 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 step 14). If connection is faulty, go to step 5).
  14. Using DVOM, check 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 connector SP201 (located between DLC and left side of instrument panel, below fuse block). Check for proper connection of Class-II serial data circuit and terminal "A" (Purple wire) of splice connector. If connection is okay, go to next step. If connection is faulty, go to step 5).
  17. Check resistance between DLC terminal No. 2 (Purple wire) and splice connector SP201 terminal "A" (Purple sire). If resistance is 0-5 ohms, go to next step. If resistance is not 0-5 ohms, go to step 29).
  18. Check 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 switch to RUN position. Check voltage between DLC terminals No. 2 (Purple wire) and No. 4 (Black wire). If voltage reading is 0-1 volt, go to next step. If voltage reading is not 0-1 volt, go to step 27).
  20. Turn ignition off. Using Terminal Adapter Kit (J356516-A), connect appropriate terminal adapter to splice pack SP201. Connect a jumper wire between splice pack terminal "A" and to terminal connected to affected module in splice pack. Turn ignition switch to RUN position. 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-II 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 SP201 terminal to Class-II serial data circuit for the disconnected module to ground. If resistance is infinite, go to next step. If resistance is not infinite, go to step 28).
  23. Turn ignition switch to RUN position. Check voltage from class 2 serial data circuit of the disconnected module to ground. If voltage reading is 0-1 volt, go to next step. If voltage reading is not 0-1 volt, go to step 27).
  24. Turn ignition off. Inspect connector of disconnected module in the area of the Class-II 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 SP201. Reconnect all modules on Class-II serial data link. Turn ignition switch to RUN position. 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 SP201 and module that does not communicate. After repairs, go to step 31).
  27. Turn ignition off. Repair short to voltage in Class-II serial data circuit. After repairs, go to step 31).
  28. Repair short to ground in class 2 serial data circuit. After repairs, go to step 31).
  29. Repair open in class 2 serial data circuit. After repairs, recheck system operation.
  30. Repair open in Black/White wire between DLC and BBEC. After repairs, recheck system operation.
  31. Reconnect splice connector SP201 and all modules on the class 2 serial data link. Turn ignition switch to RUN position. Wait 10 seconds. Check for DTCs in each module on the class 2 serial data link. If any current "U" codes/DTCs are present, go to step 33). If no current "U" codes/DTCs are present, go to next step.
  32. If other DTCs are set (not "U" code), go to next step. If "U" codes/DTCs are set, go to step 34).
  33. Diagnose DTC(s) set. Go to appropriate DTC diagnosis. After diagnosing DTC(s) go to step 35).
  34. Diagnose DTCs. After diagnosing DTC(s), go to next step.
  35. Clear all DTCs. After clearing DTCs, recheck system operation.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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