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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 405 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0420: TWC System - Low Efficiency >> Diagnostic Procedures

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. NOTE: If any other DTCs are set, diagnose the other DTCs first.
  2. Are any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Inspect the exhaust system for leaks, damage, loose, or missing hardware. If the condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step  6. If no, go to next step.
  4. Inspect for the following conditions:
    • The correct original equipment catalytic converter is installed.
    • The converter for damage such as dents, severe discoloration, holes, etc.
    • Properly installed oxygen sensors.
    • Damaged wiring, or improper connections.

    If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step  6. If no, go to next step.

    5. NOTE: In order to avoid damaging the replacement 3 way catalytic converter, correct the engine misfire or mechanical fault before replacing the 3 way catalytic converter.
  5. Replace the catalytic converter. Did you complete the repair? If yes, go to next step.
  6. 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.
  7. 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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