Originally Posted by
Vladi17
Okay, this is my least favorite number. This is my third time recieving this code within 9 months. The first time I replaced the o2 sensor before the monifold. I then got the same error three months after and replaced my other oxygen sensor along with the previous one. Therefore I have had two new o2 sensors in my car for the last 3 months. They are the bosch universal ones. I read after installing that those aren't the best to get, but they are the cheapest. Anyway, I am now wondering if my cat is bad and what I should do about these stinkin o2 sensors. Please help me fix this problem so it won't come back again.
Thanks, Andrew
I had the same problem with my 2000 Honda Civic EX automatic. P0420 COULD be bad 02 Sensors OR it could be the Catalytic converter! I replaced my 02 Sensor and light stayed on. So replaced the Catalytic converter and Cleaned out both 02 Sensors and problem solved!! Civic EX Cats are cheap to replace ($270). Civic LX and DX and CX have catalyctic converter connected to exhaust manifold as ONE PART and that alone costs $960 at hte DEALERSHIP!! Take it form a used car dealer, I've had many of these.