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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 101 (Engine Control System Self-Diagnostics - 3.4L) >> Diagnostic Tests >> DTC P0420: TWC System Low Efficiency (Bank 1) >> Test Description

Test Description

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The numbers below refer to the step numbers in the diagnostic procedures.

  1. 2

    If any component DTCs are set, diagnose those DTCs first. A fault in a component can cause the TWC to appear degraded or may have caused the TWC failure.

  2. 3

    Clearing the DTCs allows the catalyst test to be completed up to 6 times this ignition cycle. If the A/C is not turned OFF the diagnostic will not run. The engine must be warmed-up. The TWC needs to be warmed-up by raising the engine speed greater than idle for the specified time prior to each attempted test. Verify if DTC passed or failed this ignition cycle. If the DTC does not pass or fail look for a possible reason that would cause the test to abort.

  3. 4

    This step includes tests for conditions that can cause the TWC to appear degraded. Repair any problems found before proceeding with this diagnostic procedure.

  4. 9

    If the TWC needs to be replaced, ensure that another condition which could damage the TWC is not present. Conditions may include misfire, high engine oil or coolant consumption, retarded spark timing, a weak spark, or a rich or lean fuel system. Correct any possible causes of TWC damage before replacing the converter.
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