I recently purchased a 2004 honda civic ex coupe. The check engine light came on. I took it to a mechanic, he said it was a bad cat. convertor. He replaced. however, when I was driving it home the check engine light came back on. I took it to autozone and they checked the code P04020 bank 1. Does anyone have any suggestions on what the problem is and how to fix. This vehicle was in a flood 1" up on the floor board of the vehicle.

 

P0420 is the code that means bad catalytic converter, reset it and see if it doesn't come back on (might take a couple weeks). If it does come back it's probably your second oxygen sensor

 

mxs,
Thanks for the reply. I had the code reset twice. Once yesterday and again today. It came back on quickly both times, the later only after 5 miles of driving. Is the second O2 sensor in the front at the manifold or else where? How easy is it to change?
Thanks, Robbie

 

it's in the cat, just take it back to the place that replaced the cat and have them look at it again.

 

I took back, the cat is brand new with no problems according to the mechanic. he suggested a vacuum leak or O2 sensors? any help?