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?
When you erase a code by removing a battery cable, the computer has to relearn your engine so it will run a little different for a few miles, it take about 10 min just to lean to idle it correctly.
A crack in the manifold will definitely set this code.
You only have one bank. If you had a vee engine (V-6 or V-8), then you would have two banks, one would be designated bank one and the other bank two. Each bank has two O2 sensors, sensor 1 is the front sensor located before the cat, sensor 2 is the rear sensor located behind the cat. When this code is caused by a faulty sensor, it is usually the rear sensor.
The only way to repair a cracked exhaust manifold is to replace it or to remove it and have it welded. And I agree that it’s very likely what’s causing the code.
As a test, you can try using muffler repair goop. It generally comes in a tube with a woven cloth to the used like fiberglass. I’ve used it to temporarily repair a rot hole in a cat converter and it held up well. It may hold up well enough on the manifold crack to enable you to determine if the code will stay cleared. I’m not recommending it as a permanent repair, but if it holds up…let us know.