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Home >> Chevrolet >> 2000 >> C3500 HD 6.5 F, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - Diesel >> Diagnostic Tests >> DTC P1635: Pcm 5-Volt Reference Low >> 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. Connect scan tool. Crank engine for 15 seconds or until engine starts. Check if DTC P1635 sets. If DTC P1635 sets, go to next step. If DTC P1635 does not set, go to step  5.
  3. Turn ignition off. Disconnect boost sensor harness connector. Turn ignition on. Measure voltage between ground and 5-volt reference circuit at boost sensor harness connector. If voltage is less than 4 volts, go to next step. If voltage is not less than 4 volts, go to step  6.
  4. Turn ignition off. Disconnect PCM harness connector containing boost sensor 5-volt reference circuit. Using test light connected to battery positive, probe boost sensor 5-volt reference circuit at PCM harness connector. If test light illuminates, go to step  7. If test light does not illuminate, go to step  8.
  5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS . If any additional DTCs are set, perform appropriate DTC test.
  6. Replace boost sensor. See BOOST PRESSURE SENSOR  After repairs, go to step  12.
  7. Ensure test light is still connected to boost sensor 5-volt reference circuit at PCM harness connector. Disconnect sensors, one at a time, that share 5-volt reference with boost sensor. If test light turns off when one of the sensors are disconnected, go to step  9. If test light does not turn off when one of the sensors are disconnected, go to step  10.
  8. Turn ignition off. Disconnect PCM harness connector containing optical/fuel temperature sensor 5-volt reference circuit. Using test light connected to battery positive, probe optical/fuel temperature sensor 5-volt reference circuit at PCM harness connector. If test light illuminates, go to step  10. If test light does not illuminate, go to step  11.
  9. Replace sensor that caused test light to turn off. After repairs, go to step  12.
  10. Repair short to ground in 5-volt reference circuit. After repairs, go to step  12.
  11. Replace PCM. Perform PCM relearn procedures. See PROGRAMMING . After repairs, go to next step.
  12. Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P1635. 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.
  13. 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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