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Home >> Pontiac >> 2000 >> Firebird Formula, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 5.7L >> Diagnostic Tests >> DTC P1635: 5-Volt Reference No. 1 Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Start and operate engine at idle for 2 minutes. Using scan tool, monitor DTC. If both DTCs P1635 and P1639 fails this ignition, go to step  5. If only DTC P1639 did not fail this ignition, go to next step.
  3. If DTC P1635 failed this ignition, go to step  9. If DTC P1635 did not fail this ignition, go to next step.
    NOTE: If DTCs P1635 and P1639 are present, go to step  5. If only DTC P1635 is present, go to step  9.
  4. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC and observe parameters. Turn ignition off for 15 seconds. Start engine. Operate vehicle within conditions for setting this DTC and as close to conditions recorded in Freeze Frame/Failure Records. Select DTC option, SPECIFIC DTC option, then enter this DTC on scan tool. Select DTC P1635 and P1639 to determine if both DTCs set at the same time. If scan tool indicates that DTC P1635 or P1635 and P1639 set in this ignition, go to next step. If scan tool does not indicate that DTC P1635 or P1635 and P1639, see DIAGNOSTIC AIDS .
  5. Allow engine to idle. Using scan tool, monitor voltages for fuel level sensor(s), fuel tank pressure sensor, EGR pintle position sensor, TP sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the voltage reading is 5 volts or greater, go to step  18. If any of the voltage reading is not 5 volts or greater, go to next step.
  6. Turn ignition off, with engine off. Using scan tool, monitor voltages for fuel level sensor(s), fuel tank pressure sensor, engine oil pressure sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the voltages increase when fuel pump was turned on, go to step  11. If any of the voltages does not increase when fuel pump was turned on, go to next step.
  7. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and each 5-volt reference circuit at PCM harness connector for fuel tank pressure sensor, engine oil pressure sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the circuits measure greater than 5.1 volts, go to step  12. If any of the circuits does not measure greater than 5.1 volts, go to next step.
  8. Turn ignition off. Remove fuses to PCM ignition and BCM battery. Disconnect harness connectors to MAP, TP, EGR, fuel level, fuel tank pressure and A/C refrigerant pressure sensors. Check resistance between each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If any of the circuits indicate a resistance of 0-2 ohms, go to step  13. If any of the circuits does not indicate a resistance of 0-2 ohms, go to step  15.
  9. Turn ignition off. Disconnect PCM harness connector. Using test light connected to battery voltage, probe test light to PCM harness connector 5-volt reference circuits to MAP and EGR sensors. If test light illuminates on any of the circuits, go to step  14. If test light does not illuminate on any of the circuits, go to next step.
  10. Check resistance from each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If any of the circuits indicate a resistance of 0-2 ohms, go to step  13. If any of the circuits does not indicate a resistance of 0-2 ohms, go to step  15.
  11. Repair short between fuel pump circuit and appropriate 5-volt reference circuit. After repairs, go to step  19.
  12. Repair short to voltage on appropriate 5-volt reference circuit. After repairs, go to step  19.
  13. Repair short to voltage between appropriate 5-volt reference circuit and PCM circuit that had continuity. After repairs, go to step  19.
  14. Repair short to ground on appropriate 5-volt reference circuit. After repairs, go to step  19.
  15. Reconnect PCM harness connector. Using scan tool, clear DTCs. Start and operate engine at idle. Using scan tool, monitor DTCs while disconnecting the following components one at a time: MAP, TP, EGR, fuel level, fuel tank pressure and A/C refrigerant pressure sensors. If scan tool indicates that DTC P1635/P1639 passed with component disconnected, go to next step. If scan tool does not indicate that DTC P1635/P1639 passed with component disconnected, go to step  17.
  16. Replace components for which DTC passed. After replacing component, go to step  19.
  17. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  18. Repair short to voltage on appropriate signal circuit. After repairs, go to next step.
  19. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within 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 function. If any undiagnosed DTCs are displayed, go to applicable DTC test.
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