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Home >> GMC >> 1998 >> Forward Control 6.5 F >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 6.5L Turbo Diesel >> Diagnostic Trouble Codes >> DTC P0370 - Timing Reference High Resolution >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Turn ignition off. Disconnect optical/fuel temperature sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between 5-volt reference circuit of optical sensor connector and ground. 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. Using a test light connected to battery voltage, probe ground circuit of optical sensor 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 on Hz scale, backprobe high resolution signal circuit at PCM. If DVOM reading is 3740-3940 Hz, go to step 16). If DVOM reading is not 3740-3940 Hz, go to step 9).
  6. Turn ignition off. Disconnect PCM harness connector. 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 for open or poor connections at sensor ground terminals of PCM. Repair as necessary. After repairs, go to step 19). If connections are okay, go to step 18).
  8. Check optical sensor 5-volt reference circuit for proper connection at PCM connector. 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, with engine off. Using DVOM check voltage between ground and sensor harness connector high resolution signal circuit. If voltage reading is 4.8-5.2 volts, go to step 13). If voltage reading is not 4.8-5.2 volts, go to next step.
  10. If voltage reading was greater than 4.8-5.2 volts, go to next step. If voltage reading was less 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 connector. Check high resolution signal circuit for an 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 in mA (milliamp) scale, check current between high resolution signal circuit and ground circuit at optical/fuel temperature sensor harness connector. If reading is less than 50 mA, go to step 15). If reading is 50 mA, go to next step.
  14. Repair short to reference signal voltage on 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 circuit is okay, go to step 17).
  16. Turn ignition off. Disconnect PCM harness connector. Check high resolution signal circuit for proper connection at PCM. Repair as necessary. After repairs, go to step 19). If circuit is okay, go to step 18).
  17. Replace injection pump. If fuel injection pump is replaced, new pump must be timed. See appropriate ON-VEHICLE ADJUSTMENTS article. After replacing injection pump, go to step 19).
  18. Replace PCM. After replacing PCM, go to next step.
  19. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, 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, repeat step 2).
  20. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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