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Home >> Buick >> 2003 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 3.1L Engine >> Diagnostic Tests >> DTC P0404: EGR Open Position Performance >> Diagnostic Procedure

Diagnostic Procedure

  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Is DTC P0403 or P0405 also set? If yes, diagnose appropriate DTC. Go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
  3. Turn ignition switch to RUN position, engine OFF. Command the EGR valve from zero percent to 100 percent using a scan tool. Does the EGR position sensor parameter remain within 15 percent of the desired EGR Position parameter when commanded using a scan tool? If yes, go to next step. If no, go to step  5.
  4. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within the Conditions For Running Test. See CONDITIONS FOR RUNNING TEST . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  5. Turn ignition switch to OFF position. Disconnect the EGR valve. Turn ignition switch to RUN position, engine OFF. Observe the EGR position sensor parameter using a scan tool. Is the EGR position sensor parameter less than one percent? If yes, go to next step. If no, go to step  11.
  6. Connect a test light between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve Does the test light illuminate? If yes, go to next step. If no, go to step  8.
  7. Connect a 3 amp fused jumper wire between the 5-volt reference circuit of the EGR valve and the EGR valve position signal circuit. Observe the EGR POSITION SENSOR parameter on the scan tool. Is the EGR Position Sensor parameter more than 99 percent? If yes, go to step  9. If no, go to step  13.
  8. Connect a test light between the 5-volt reference circuit of the EGR valve and a good ground. Does the test light illuminate? If yes, go to step  12. If no, go to step  14.
    9. NOTE: If the scan tool output control function times out, re-command the EGR valve to 100 percent before the next electrical measurement is taken.
  9. Command the EGR valve to 100 percent using a scan tool. Measure the voltage from the EGR high control circuit to a good ground. Note the results in volts as "supply voltage". Connect a jumper wire between the EGR low control circuit and the corresponding terminal on the EGR valve. Connect a DMM between the EGR high control circuit and the corresponding terminal on the EGR valve. Measure the note and current draw in amps. Remove the DMM from the EGR high control circuit. Connect a jumper wire between the EGR high control circuit and the corresponding terminal on the EGR valve. Connect a DMM in parallel between the EGR high control circuit and a good ground. Measure the voltage drop in volts and note as "load voltage drop". Subtract the load voltage drop from the supply voltage then divide the answer by the current draw. The result is the amount of resistance in the EGR high control circuit. Is the calculated resistance more than 3 ohms? If yes, go to step  15. If no, go to next step.
    10. NOTE: If the scan tool output control function times out, re-command the EGR valve to 100 percent before the next electrical measurement is taken.
  10. Connect a DMM in parallel between the EGR low control circuit and a good ground. Measure the voltage drop in volts and not as "low control voltage drop". Divide the low control voltage drop by the current draw. The result is the amount of resistance in the low control circuit. Is the calculated resistance more than 3 ohms? If yes, go to step  16. If no, go to step  17.
  11. Test the EGR valve position signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.
  12. Test the low reference circuit of the EGR valve for an open or for high resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.
  13. Test the EGR valve position signal circuit for the following conditions:
    • An open.
    • A short to ground.
    • High resistance.

    Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.

  14. Test the 5-volt reference circuit of the EGR valve for an open or for high resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.
  15. Test the high control circuit of the EGR valve for resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.
  16. Test the low control circuit of the EGR valve for resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.
  17. Test for an intermittent and for a poor connection at the EGR valve. Did you find and correct the condition? If yes, go to step  21. If no, go to step  19.
  18. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  19. Replace the EGR valve. After repair, go to step  21.
  20. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repair, go to next step.
  21. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See CONDITIONS FOR RUNNING TEST . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  22. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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