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Home >> GMC >> 1996 >> Forward Control 4.3 W >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - P Series (6.5L Diesel) >> Diagnostic Trouble Codes >> DTC P0370 - Timing Reference High Resolution >> Diagnostic Procedures
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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 5 volts, go to next step. If voltage is not 5 volts, go to step 5).
  3. Using test light, probe ground circuit of optical sensor connector to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  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 10). If DVOM reading is not 3740-3940 Hz, go to step 9).
  5. Remove electrical harness filter from vehicle. Using DVOM, check resistance at terminal "A" (5-volt reference circuit) of electrical harness filter. If resistance is greater than 2 ohms, go to step 13). If resistance is less than 2 ohms, go to next step.
  6. Turn ignition off. Leave electrical harness filter removed from vehicle. Disconnect PCM connector. Check 5-volt reference circuit for open, short to ground, or short to sensor ground circuit. Repair as necessary. If 5-volt reference circuit is open or shorted to ground, go to step 14). If 5-volt reference circuit is not open or shorted to ground, go to step 8).
  7. Check for open or poor connections at sensor ground terminals of PCM. Repair as necessary. If a problem was found, go to step 14). If a problem was not found, go to step 12).
  8. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. If any terminals were replaced, go to step 14). If no terminals were replaced, go to step 12).
  9. Turn ignition off. Check for open or short to ground in high resolution signal circuit. Repair as necessary. If high resolution signal circuit is open or shorted to ground, go to step 14). If high resolution signal circuit is not open or shorted to ground, go to step 11).
  10. Check for poor connections at high resolution signal terminals of PCM. Repair terminals as necessary. If any terminals were replaced, go to step 14). If no terminals were replaced, go to step 12).
  11. Replace injection pump. If fuel injection pump is replaced, new pump must be timed. See appropriate ADJUSTMENTS article. Go to step 14).
  12. Replace PCM. Go to step 16).
  13. Replace electrical harness filter. Go to next step.
  14. 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).
  15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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