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Home >> GMC >> 2000 >> C3500 HD 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - Diesel >> Diagnostic Tests >> DTC P0251: Injection Pump Cam System >> Diagnostic Procedures

Diagnostic Procedures

  1. If OBD system check has been performed, go to next step. If OBD system check has not been performed, see ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Check if DTC P0370 is also set. If DTC P0370 is set, diagnose DTC P0370 first. If DTC P0370 is not set, go to next step.
  3. Start and idle engine. Using scan tool, with throttle closed, observe CAM REF MISSED display. If scan tool displays "8", go to step  5. If scan tool does not display "8", go to next step.
  4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS . If any additional DTCs are set, perform appropriate DTC test.
  5. Turn ignition off. Disconnect optical/fuel temperature sensor harness connector. Turn ignition on. Measure voltage between ground and 5-volt reference circuit at optical/fuel temperature sensor harness connector. If voltage is 4.8-5.2 volts, go to next step. If voltage is not 4.8-5.2 volts, go to step  8.
  6. Using test light connected to battery positive, probe ground circuit at optical/fuel temperature sensor harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  9.
  7. Reconnect optical/fuel temperature sensor harness connector. Start and idle engine. Using scan tool, command engine speed to 900 RPM. Using DVOM set to Hz scale, backprobe cam signal circuit at PCM harness connector. If DVOM indicates 57-63 Hz, go to step  15. If DVOM does not indicate 57-63 Hz, go to step  11.
  8. Turn ignition off. Disconnect PCM harness connectors. Check 5-volt reference circuit for open, short to ground or short to sensor ground circuit. Repair as necessary. After repairs, go to step  21. If circuit is okay, go to step  10.
  9. Check for open or poor sensor ground terminal connection at PCM. Repair as necessary. After repairs, go to step  21. If circuit and connection is okay, go to step  20.
  10. Check optical/fuel temperature 5-volt reference circuit for poor connection at PCM. Repair as necessary. After repairs, go to step  21. If connection is okay, go to step  20.
  11. Turn ignition on. Disconnect optical/fuel temperature sensor harness connector. Measure voltage between ground and CAM signal circuit of optical/fuel temperature sensor harness connector. If voltage is 4.8-5.2 volts, go to step  16. If voltage is not 4.8-5.2 volts, go to next step.
  12. If voltage range is greater than 4.8-5.2 volts, go to next step. If voltage range is not greater than 4.8-5.2 volts, go to step  14.
  13. Repair short to battery/ignition voltage in CAM signal circuit. After repairs, go to step  21.
  14. Turn ignition off. Check for open or short to ground in CAM signal circuit. Repair as necessary. After repairs, go to step  21. If circuit is okay, go to next step.
  15. Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step  21. If connections are okay, go to step  20.
  16. Using DVOM set to milliamp (mA) scale, measure current between CAM signal circuit and ground circuit of optical/fuel temperature sensor harness connector. If reading is less than 50 mA, go to step  18. If reading is not less than 50 mA, go to next step.
  17. Repair short to reference voltage in CAM signal circuit. After repairs, go to step  21.
  18. Check for poor connections at injection pump. Repair as necessary. After repairs, go to step  21. If connections are okay, go to next step.
  19. Replace injection pump. After replacement, new pump must be timed. See appropriate ON-VEHICLE ADJUSTMENTS article. After repairs, go to step  21.
  20. Replace PCM. Perform PCM relearn procedures. See PROGRAMMING . After repairs, go to next step.
  21. Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0251. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step  2.
  22. Using scan tool, check for DTCs. If any undiagnosed DTCs are set, perform appropriate DTC test. If no DTCs are set, system is okay.
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