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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Is DTC P0403 or P0405 also set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Turn ignition on, with engine off. Command the EGR valve from zero percent to 100 percent with a scan tool. Does the EGR POSITION SENSOR parameter remain within 8 percent of the DESIRED EGR POSITION parameter when commanded with a scan tool? If yes, go to next step. If no, go to step  5.
  4. Observe the Freeze Frame/Failure Records for this DTC. Turn off the ignition for 30 seconds. Operate the vehicle within the Conditions For Running DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. Turn ignition off. Disconnect the EGR valve. Turn ignition on, with engine off. Observe the EGR POSITION SENSOR parameter with a scan tool. Is the EGR POSITION SENSOR parameter less than 1 percent? If yes, go to next step. If no, go to step  11.
  6. Connect a test light between the EGR valve 5-volt reference circuit and the EGR valve low reference circuit. 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 EGR valve 5-volt reference circuit 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  14.
  8. Connect a test light between the EGR valve 5-volt reference circuit 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. Perform the following checks:
    • Command the EGR valve to 100 percent with 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 DVOM between the EGR high control circuit and the corresponding terminal on the EGR valve.
    • Measure and note the current draw in amps.
    • Remove the DVOM 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 DVOM 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. Perform the following checks:
    • Connect a DVOM 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 an open, a short to ground or 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 EGR valve high control circuit for high resistance. Did you find and correct the condition? If yes, go to step  21. If no, go to step  18.
  16. Test the EGR valve low control circuit for high 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/or poor connections 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/or poor connections at the PCM. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  19. Replace EGR valve. See EGR VALVE under EMISSION SYSTEMS & SUB-SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  21.
  20. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to next step.
  21. Clear the DTCs with a scan tool. Turn off the ignition for 30 seconds. Start the engine and operate vehicle within the Conditions For Running DTC. You may also operate vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to step  2. If no, go to next step.
  22. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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