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Home >> GMC >> 1997 >> Forward Control 6.5 F >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Engine Testing - 6.5L Diesel (P Series) >> On-Board Diagnostic (OBD) System Check >> DLC Diagnosis Or No Scan Tool Data

DLC Diagnosis Or No Scan Tool Data

  1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Turn ignition off for 30 seconds. Turn ignition on with engine off. Observe MIL. If MIL illuminates, go to next step. If MIL does not illuminate, go to MALFUNCTION INDICATOR LIGHT (MIL) .
  3. Install scan tool. If scan tool communicates with PCM, go to next step. If scan tool does not communicate with PCM, go to step 7).
  4. Install Tech 1 scan tool. Turn ignition on. Using scan tool, command MIL to turn on and off. If MIL turns on and off as commanded, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . If MIL does not turn on and off as commanded, go to next step.
  5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. If Malfunction Indicator Light (MIL) illuminates, go to step 17). If MIL does not illuminate, go to next step.
  6. Using scan tool, check engine calibration ID. If proper ID is displayed, go to step 26). If proper ID not displayed, go to step 18).
  7. Connect a test light to ground. Using test light, probe DLC terminal No. 16. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 19).
  8. Connect a test light to battery voltage. Using test light, probe DLC terminals No. 4 and 5. See the WIRING DIAGRAMS article. If test light illuminates on both circuits, go to next step. If test light does not illuminate on either circuit, go to step 20).
  9. Check cigarette lighter for power. If power is present at cigarette lighter, go to next step. If power is not present at cigarette lighter, go to step 21).
  10. Install and check scan tool on another vehicle. If scan tool works, go to next step. If scan tool does not work, go to step 22).
  11. Disconnect scan tool. Using DVOM, check voltage between ground and PCM serial data line at DLC terminal No. 2. See the WIRING DIAGRAMS article. If voltage is less than 7 volts, go to next step. If voltage is 7 volts or greater, go to step 15).
  12. Using DVOM, again check voltage between ground and DLC terminal No. 2. If voltage is less than one volt, go to next step. If voltage is one volt or greater, go to step 16).
  13. Turn ignition off. Using DVOM, check resistance between ground and DLC terminal No. 2. If resistance is less than 10 ohms, go to next step. If resistance is 10 ohms or greater, go to step 25).
  14. Disconnect PCM connectors. Using DVOM, check resistance between ground and DLC terminal No. 2. If resistance is less than 10 ohms, go to step 23). If resistance is 10 ohms or greater, go to step 26).
  15. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Check voltage on DLC terminal No. 2. Voltage should not be present. If voltage is not as specified, go to step 24). If voltage is as specified, go to step 26).
  16. Reprogram EEPROM and retest. If serial data is present, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . If serial data is not present, go to step 26).
  17. Repair short to ground in MIL control circuit. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  18. Reprogram EEPROM and retest. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  19. Check fuse No. 7 (PWR AUX). If fuse is faulty, repair short to ground in DLC terminal No. 16 circuit. If fuse is okay, repair open in DLC terminal No. 16 circuit. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  20. Repair open in affected circuit. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  21. Repair cigarette lighter circuit. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  22. Repair or replace faulty scan tool and/or cables. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  23. Repair short to ground in serial data line. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  24. Repair short to voltage in serial data line. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  25. Check for open in serial data line. If circuit is okay, check PCM and DLC connectors. If connectors are okay, replace PCM. Perform PCM relearn procedures. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
  26. Replace PCM. Reprogram replacement PCM. After replacing PCM, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .
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