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Home >> GMC >> 1997 >> Forward Control 6.5 F >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 6.5L Diesel (P Series) >> Diagnostic Trouble Codes >> DTC P0370 - Timing Reference High Resolution >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING article. Then 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 5 volts, go to next step. If voltage is not 5 volts, go to step 5).
  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 8).
  4. Reconnect optical/fuel temperature sensor connector. Start and idle engine. Using scan tool, command engine speed to 900 RPM. Using DVOM on Hz scale, backprobe high resolution signal circuit of PCM. If DVOM reading is 3740-3940 Hz, go to step 11). If DVOM reading is not 3740-3940 Hz, go to step 10).
  5. If vehicle is equipped with an electrical filter harness at the optical sensor, go to next step. If vehicle is not equipped with and electrical filter, go to step 7).
  6. Remove electrical harness filter from vehicle. Using DVOM, check resistance of filter. If resistance is greater than 2 ohms, go to step 14). If resistance is less than 2 ohms, go to next step.
  7. Turn ignition off. Leave electrical harness filter removed from vehicle. 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 15). If circuit is okay, go to step 9).
  8. Check for open or poor connections at sensor ground terminals of PCM. Repair as necessary. After repairs, go to step 14). If connections are okay, go to step 12).
  9. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 15). If terminals are okay, go to step 13).
  10. Turn ignition off. Check for open or short to ground in high resolution signal circuit. Repair as necessary. After repairs, go to step 15). If circuit is okay, go to step 12).
  11. Check for poor connections at high resolution signal terminals of PCM. Repair terminals as necessary. After repairs, go to step 15). If terminals are okay, go to step 13).
  12. Replace injection pump. If fuel injection pump is replaced, new pump must be timed. See the ADJUSTMENTS article. After replacing injection pump, go to step 15).
  13. Replace PCM. After replacing PCM, go to step 15).
  14. Replace electrical filter. After replacing filter, go to next step.
  15. 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).
  16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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