Hi,
I recently purchased a Honda Civic 2001 EX with 136K miles. The check engine light was on with two codes for faulty o2 sensors 1 and 2. I replaced both sensors recently and now this p0420 code showed up! I know this code usually means a bad catalytic convertor and I'm assuming since the previous owner ignored replacing both o2 sensors, it may have caused some damage to the catalytic, right?

The car runs fine with no issues or rattling. I get a little over 35mpg which I think is a good sign that at least the convertor is not clogged. I should mention though that the new o2 sensors are different brands (Bosch and Denso) and I don't know if that would cause the code to appear?

For how long I can ignore this problem and shall I look into other causes other than an efficient convertor? I live in MN and there are no requirements for emission test. In the case if I need to replace the convertor soon, what are the best aftermarket options I should look into?

Thank you

 

Both O2 sensors must be functioning in order for the ECU to monitor the condition of the cat, which has likely been toast for some time.

 

You're everywhere, You're Awesome lol

I too replaced my O2 sensor, I think it's usually reffered to a Air Sensor? The Bank 1 Sensor 1, Upstream Sensor. I replaced it with the following one;


I removed Fuse 15 under my hood, which is the ECU. Yet the CEL goes away then comes back on after some driving. Any clue on what may be causing this? Perhaps i don't have the correct part on it?

 

P0132 Sensor Circuit High Voltage (Bank 1 Sensor 1)

That;s what i get on my scanner