hello,

first time user, just bought an 03 civic ex 135k that has MIL on for a P0420. Exhaust smells very rich, its this pretty straight forward a catalytic converter? has it more commonly been the pre cat at the manifold or the one under the car? If 02 sensors were bad would they throw codes individually? i want to order parts today and want to make sure im going the right direction. Not sure if i need to replace both sections of the CC and o2 sensors or should i start somewhere else?

Car runs great otherwise, fuel economy isnt too great, around 30mpg.


thanks again for any help!