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Home >> Pontiac >> 2003 >> Aztek AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0420: TWC System - Low Efficiency >> Diagnostic Procedures
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Diagnostic Procedures

  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. Are any other DTCs set? If yes, diagnose affected DTCs first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
    3. NOTE: If the A/C is left ON, the following diagnostic may not run. If more than 6 tests have been attempted and the DTC has not passed or failed this ignition cycle, the test may be aborting. See DIAGNOSTIC AIDS .
  3. Clear the DTCs using the scan tool. Turn the A/C OFF. Start engine and wait until the vehicle is fully warmed up. Fully open the hood. Operate the vehicle within the Conditions for Running this DTC. See CONDITIONS FOR RUNNING DTC . The test may need to be completed up to 6 times in order to pass or fail. Does the scan tool indicate the DTC ran and passed this ignition cycle? If yes, system is okay. If no, go to next step.
  4. Visually and physically inspect the TWC for damage. Inspect for the following conditions:
    • Dents.
    • Severe discoloration caused by excessive temperatures.
    • Holes.
    • Internal rattle caused by damaged catalyst substrate.
    • Verify that the TWC is a proper original equipment manufacturer part.

    Did your inspection reveal a problem? If yes, go to step  9. If no, go to next step.

  5. Visually and physically inspect the exhaust system for leaks. Did your inspection reveal a problem? If yes, go to step  7. If no, go to next step.
  6. Visually inspect the following components for damage:
    • Oxygen sensors.
    • Oxygen sensor wiring harnesses.

    Was a repair necessary? If yes, go to step  8. If no, go to step  9.

  7. Repair exhaust system as necessary. After repairs, go to step  10.
  8. Repair HO2S sensor and wiring as necessary. After repairs, go to step  10.
    9. NOTE: A misfiring condition may damage the replacement TWC converter. Check for a misfiring condition. If a misfire is present, repair the misfiring condition before replacing the TWC converter.
  9. Replace the TWC converter. After repairs, go to next step.
    10. NOTE: If the A/C is left ON, the following diagnostic may not run. If more than 6 tests have been attempted and the DTC has not passed or failed this ignition cycle, the test may be aborting. See DIAGNOSTIC AIDS .
  10. Clear the DTCs using the scan tool. Turn the A/C OFF. Start engine and wait until the vehicle is fully warmed up. Fully open the hood. Operate the vehicle within the Conditions for Running this DTC. See CONDITIONS FOR RUNNING DTC . The test may need to be completed up to 6 times in order to pass or fail. Does the scan tool indicate the DTC ran and passed this ignition cycle? If yes, go to next step. If no, go to step  4.
  11. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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