Test Description

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 its 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 may not run. The engine must be warmed-up. The TWC needs to be warmed-up by raising the engine speed above idle for the specified time prior to each attempted test. Inspect and see if the 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.
4. 9 -  If the TWC needs to be replaced, make sure that another condition is not present which could damage the TWC. These conditions may include misfire, high engine oil or coolant consumption, retarded spark timing, weak spark, or a rich or lean fuel system. Correct any possible causes of TWC damage before replacing the TWC.