As the title says I have a 2000 Honda Civic. Recently the check engine light came on and i had it checked out. the code that came back was P0420, Catalyst system efficiency below threshold bank 1. Probable cause: Air/Fuel ratio concern, Air leak near HO2( Heated O2 sensor) Bank 1, Ignition system concern, or Faulty catalytic converter. After getting this I got home and reset everything on my car by removing the positive terminal. After that I started the car to watch the revs while resetting my radio. The car started to idle low at about 500rpms, it would creep up to about 750rpm and then there would be a clicking noise and the revs would drop back to 500rpms. this didnt happen before I reset the car.
Is this Just my O2 sensor or is it the converter?
Also I replaced the the upper O2 sensor about six months ago and noticed a crack in the exhaust manifold. Is that the issue or is it the lower O2 this time?
Final question is, what is Bank 1?