Some Toyota Corolla owners report experiencing catalytic converter issues related to engine oil burning, which can lead to the triggering of the P0420 code. These owners note that oil contamination from engine oil breakdown can compromise the catalytic converter's efficiency, signaling a potential failure. Common symptoms include a decline in catalytic converter performance, indicating possible oil contamination. To prevent future issues, it is essential for owners to address underlying engine problems, such as oil consumption, which can help mitigate the recurrence of the P0420 code. Additionally, resolving the catalytic converter issue may require changing the engine oil and filter to eliminate the effects of burning oil. Prompt action is crucial to maintain the health of the catalytic converter and prevent further damage.

You may be able to prevent automatic transmission problems by servicing the transmission and inspecting the fluid every 30,000 miles. If the fluid is dark or burned, the transmission system should be completely flushed.