So my CEL is on with a P0422 code (Main Catalyst Efficiency Below Threshold). I can smell exhaust in the cabin and behind the car. The smell inside isn't overwhelming - I have asked a couple of friends and they can't smell it but I can.

I have done some research around the Internets and have come across some conflicting info.

It sounds like most popular course of action is to change the rear O2 sensor first and see what happens. If that doesn't work, the next step would be to replace the catalytic converter.

Does anyone else have some ideas? Does the exhaust smell mean anything? I have read the MAF sensor may play into this but others are insistent this isn't the case. Thanks guys for your help.

 

Generally if you can smell the exhaust more than normal than you cat is probably up for a replacement. It could be the 2nd o2 sensor but that wouldn't make it smell obviously

 

I have the same problem with my 1999 1.8t AEB. Poking around I found that p0422 is the bank one censor, This is the o2 before the CAT, p0432 is bank 2 the one after the CAT. I am also confused due to Bank one monitors the fuel air mixture. I puled my plugs and they look fine. I have no loss of power and I will have to determine if there is loss in the fuel economy. I am also going to persue the fuel that i am using.

 

You will not be able to tell if a converter is bad due to the smell. The best thing to do is if there are no other codes is to replace the cat (dealer only) & both o/2 sensors , problem fixed!