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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 51 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0420: TWC System - Low Efficiency >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. 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. Are any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, go to next step.
  3. Test the exhaust system for the following:
    • Leaks.
    • Loose or missing hardware.

    Repair as necessary. Did you find a problem? If yes, go to step  5 . If no, go to next step.

  4. Verify that the correct original equipment three-way catalytic converter is installed. Test the converter for the following:
    • Dents.
    • Severe discoloration.
    • Holes.
    • Ensure that oxygen sensors are properly installed and that wiring connections are undamaged and properly retained and not damaged.

    Repair as necessary. Did you find a problem? If yes, go to next step. If no, go to step  6 .

  5. Using the scan tool, clear the DTCs. Start the engine. Allow the engine to idle until the engine reaches normal operating temperature. Select DTC and the Specific DTC function. Enter the DTC number which was set. Operate the vehicle within the conditions for setting this DTC, until the scan tool indicates the diagnostic Ran. Does the scan tool indicate that this diagnostic Passed? If yes, system is okay. If no, go to step  2 .
    6. NOTE: In order to avoid damaging the replacement three-way catalytic converter, correct the engine misfire or mechanical fault before replacing the three-way catalytic converter.
  6. Replace the catalytic converter. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repair, system is okay.
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