DLC Diagnosis Or No Scan Tool Data

1998 Oldsmobile Achieva 3.1 M, 4T40E/MN4SECTION DLC Diagnosis Or No Scan Tool Data
WARNING: This page is about a different variant/trim than selected.
  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECKΒ  , then go to next step.
  2. Turn ignition on with engine off. Install scan tool. If scan tool is equipped with external power source, ensure power source and ground are okay. If scan tool powers up, go to next step. If scan tool does not power up, go to step 4).
  3. Disconnect scan tool. Using a test light connected to ground, probe DLC class 2 serial data circuit. See WIRING DIAGRAMS - 2.4L article. If test light does not illuminate, go to step 5). If test light illuminates, go to step 6).
  4. Using a test light connected to ground, probe DLC battery feed circuit. See WIRING DIAGRAMS - 2.4L article. If test light illuminates, go to step 7). If test light does illuminate, go to step 8).
  5. Using a test light connected to battery voltage, probe DLC class 2 serial data circuit. See WIRING DIAGRAMS - 2.4L article. If test light does not illuminate, go to step 9). If test light does illuminate, go to step 10).
  6. Check for short to voltage in class 2 serial data circuit. Repair as necessary. After repairs, go to step 17). If circuit is okay, go to step 11).
  7. Using a test light connected to battery voltage, probe DLC ground circuits. See WIRING DIAGRAMS - 2.4L article. If test light illuminates for both ground circuits, go to step 15). If test light does not illuminate for both ground circuits, go to step 12).
  8. Repair open or short to ground in DLC battery feed circuit. After repairs, go to step 17).
  9. Check for open or poor connection in class 2 serial data circuit. Repair as necessary. After repairs, go to step 17). If circuit is okay, go to step 13).
  10. Check for short to ground in class 2 serial data circuit. Repair as necessary. After repairs, go to step 17). If circuit is okay, go to next step.
  11. Replace PCM. Perform PCM relearn procedures. After repairs, go to step 17).
  12. Repair open or poor connections in DLC ground circuits. After repairs, go to step 17).
  13. Reinstall scan tool. If scan tool can communicate with PCM, go to step 17). If scan tool can not communicate with PCM, go to next step.
  14. Install scan tool on another vehicle equipped with class 2 serial data and check for proper operation. If scan tool operates properly, go to step 11). If scan tool does not operate properly, go to step 16).
  15. Check DLC for proper terminal tension or excessive resistance. Repair as necessary. After repairs, go to step 17). If terminals are okay, go to next step.
  16. Scan tool is malfunctioning. Using scan tool manual, repair as necessary. After repairs, go to next step.
  17. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and then dies, go to step 1).
  18. Warm engine to operating temperature. Check for DTCs. If DTCs are present, diagnose DTCs. If DTCs are not present, system is okay.
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When to See a Mechanic

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

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