P0420 Toyota -

Question

what should I start with first. Sometimes the car still runs great. Sometimes a little sluggish but I haven't really had a problem using it at all and still gets good fuel

Answer 1

Hi there,

Once in a while the rear o2 sensor can cause this code, and occasionally the fuel additives will do it to. Since you are experiencing a change in the way the car is running, I suggest taking the exhaust pipe down and looking into the converter to see if it's cracked inside. Usually a new converter is required to resolve the problem.