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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 133 (Engine Controls Self-Diagnostics - 4.3L) >> Diagnostic Tests >> DTC P0420: TWC System - Low Efficiency - Bank 1 & DTC P0430: TWC System - Low Efficiency - Bank 2 >> Test Description

Test Description

WARNING: This page is about a different car, the 2003 GMC Savana and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 3

    This step inspects for conditions that can cause the 3-way catalytic converter efficiency to appear degraded.

  2. 5

    A catalytic converter which has been discolored may be due to an engine running rich, lean, or had a previous sever misfire. Verifying the fuel trim percentages may be of assistance in determining if such a condition exists.

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