how can you tell on Mazda if the manifold converter or catalytic converter to be replaced

Question

we have already replaced the spark plugs and the air filter is new. recent oil change. we have reset the computer. we get error code P0421.

how can we tell which converter needs to be replaced as the manifold converter is the far more expensive repair?

thanks
JoAnne

Answer 1

Hi there,

The code is for the pre cat, the one directly off the exhaust manifold. This is the one between the 2 O2 sensors. Sorry to say but the P0420 would indicate the other converter.