Po421. On 2001 Mazda protege 5

Question

Po421code 2001 Mazda protege 5 2.0l motor

Answer 1

Hi there,

This code is for the bank 1 catalytic converter not working properly. Most of the time when this code appears the converter itself is the cause of the problem. That being said, the rear O2 sensor and any exhaust manifold leaks can also cause this code.