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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 P0370: Timing Reference High Resolution >> Diagnostic Procedures
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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. 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  6.
  3. Leave optical/fuel temperature sensor harness connector disconnected. 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  7.
  4. Reconnect optical/fuel temperature sensor harness connector. Start and operate engine as close to conditions saved in scan tool FREEZE FRAME/FAILURE RECORDS. Using scan tool, select DTC, SPECIFIC, and then enter DTC P0370. If scan tool displays "LAST TEST FAILED" message, go to next step. If "LAST TEST FAILED" message is not displayed, see DIAGNOSTIC AIDS .
  5. Maintain engine speed at point of failure as indicated in step 4)  . Using DVOM set to Hz scale, backprobe high resolution signal circuit at PCM harness connector. See HIGH RESOLUTION SIGNAL SPECIFICATIONS  table. If DVOM reading is within 100 Hz of specified value relating to RPM, go to step  16. If DVOM reading is not within 100 Hz of specified value relating to RPM, go to step  9.
  6. 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  19. If circuit is okay, go to step  8.
  7. Check sensor ground circuit for open or poor connection at PCM. Repair as necessary. After repairs, go to step  19. If circuit and connection are okay, go to step  18.
  8. Check 5-volt reference circuit for poor connection at PCM. Repair as necessary. After repairs, go to step  19. If connection is okay, go to step  18.
  9. Disconnect optical/fuel temperature sensor harness connector. Turn ignition. Using DVOM connected to ground, probe high resolution signal circuit at optical/fuel temperature sensor harness connector. If voltage is 4.8-5.2 volts, go to step  13. If voltage is not 4.8-5.2 volts, go to next step.
  10. 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  12.
  11. Repair short to battery/ignition voltage in high resolution signal circuit. After repairs, go to step  17.
  12. Turn ignition off. Disconnect PCM harness connectors. Check high resolution signal circuit for open, short to ground or short to sensor ground circuit. Repair as necessary. After repairs, go to step  19. If circuit is okay, go to step  16.
  13. Using DVOM set to milliamp (mA) scale, measure current between high resolution signal circuit and ground circuit of optical/fuel temperature sensor harness connector. If reading is less than 25 mA, go to step  15. If reading is not less than 25 mA, go to next step.
  14. Repair short to reference voltage in high resolution signal circuit. After repairs, go to step  19.
  15. Check high resolution signal circuit for poor connection at injection pump. Repair as necessary. After repairs, go to step  19. If connection is okay, go to step  17.
  16. Turn ignition off. Disconnect PCM harness connectors. Check high resolution signal circuit for poor connection at PCM. Repair as necessary. After repairs, go to step  19. If connection is okay, go to step  18.
  17. Replace injection pump. After replacement, new pump must be timed. See appropriate ON-VEHICLE ADJUSTMENTS article. After repairs, go to step  19.
  18. Replace PCM. Perform PCM relearn procedures. See PROGRAMMING . After repairs, go to next step.
  19. Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0370. 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.
  20. Using scan tool, check for DTCs. If any undiagnosed DTCs are set, perform appropriate DTC test. If no DTCs are set, system is okay.
HIGH RESOLUTION SIGNAL SPECIFICATIONS

RPM Hertz (Hz)
700 2987
800 3413
900 3840
1000 4267
1100 4693
1200 5120
1300 5547
1400 5973
1500 6400
1600 6827
1700 7253
1800 7680
1900 8170
2000 8533
2100 8960
2200 9387
2300 9813
2400 10,240
2500 10,667
2600 11,093
2700 11,520
2800 11,947
2900 12,373
3000 12,800
3100 13,227
3200 13,653
3300 14,080
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