Questions and Answers

Grand Marquis Code P0420 Q. Dear Sir; What exactly is wrong with my car, 1997, Mercury Grand Marquis, 4.6 liter, automatic transmission, fuel injection if the OBD-II code is the P0420?

I know what it supposed to be: Catalyst system efficiency below threshold (bank 1). But, I do not know what exactly does that mean. If I could take a guess could it be that the MAF (Mass air flow) sensor is failing or is dirty?

Any help will be greatly appreciated.
Carlos

A. Basically this means that the catalytic converter on that side is not doing it's job. If the exhaust system is in good shape with no leaks, then the converter is probably going bad.

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