What is the codes P0421 and P0431 catalyst efficiency below threshold Bank 1 and Bank 2 mean on a Mazda Millenia 2002?

Answer 1

The codes P0421 and P0431 indicate that the catalytic converter's efficiency is below the required threshold for Bank 1 and Bank 2 of your 2002 Mazda Millenia. This usually suggests that the catalytic converters may be failing, or there could be issues with the oxygen sensors that monitor their performance. It's advisable to inspect the exhaust system, oxygen sensors, and the condition of the catalytic converters to determine the root cause of the problem. Addressing these issues is crucial to maintaining optimal engine performance and compliance with emissions standards.