Sup HT,

 

Ouch, the dreaded 420 code. Usually it's a bad cat. I would suspect the sensor first but, you said it was recently replaced. First, look and listen for exhaust leaks. Then look for bad wires/connections. Then tap the cat LIGHTLY and listen for anything rattling around in there. If you hear stuff rattling around in the cat replace it.

 

Thanks, bro!

 

Was it an OEM replacement O2 sensor or a cheaper universal (Bosch)

 

^^ Good point.

@ dlewis2583: Did you make sure you got the right one for your engine? Remember there were like 8 different engines in that gen.

Hondas are very finicky about O2 sensors. Get Honda or Denso (OE manufacturer). You can get 'em for $150-200 at Honda or for about $55 here: http://www.rockauto.com/

 

it was universal and it was Bosch..

 

Thanks again..im on rockauto now doing some research...

 

Could a bad o2 sensor(Bosch), cause a misfire?

 

I have a similar problem. I replaced the 02 sensor with a universal sensor. The light went off but came back on after awhile. The code was P0420. Thought I was going to have to get a new cat or something. However, I put some seafoam in the tank, and in about 20 minutes the engine light went out on it's own (I never had it cleared). Thought I was in the clear but it came on again today (2 days later).

I'm confused about what is causing the light to keep coming on. I only have 140,000 miles in this civic 2001 lx. Could it just be a small clog in the cat that got temporarily cleared by the sea foam? Need to drive this car across country in a few days, so I'd appreciate help!

Thanks!

 

If it was a no name or Bosch brand beer can type of O2 sensor, they are prone to cooling off and becoming lazy. Use only Denso brand O2 sensors.

 

Always check for exhaust leaks first when replacing oxygen sensors.

 

Easiest way to tell if the code comes up because of the cat is to pull voltage readings from the o2 sensors. The code is set when the o2 voltage readings get too close to reading the same numbers.

which is the reason that putting spark pug defoulers in the rear o2 sensor will make the light go away, It changes the voltage readings enough to trick the computer into thinking the cat is working properly. And its a 6$ fix instead of the 1k+ that Honda wants for the converter.

I have an 03 Ford Escape that needed 3300$ worth of converters when I got it. (all 3) The two front converters completely emptied themselves into the rear converter due to a long term misfire. I gutted the rear converter and added spark plug defoulers to all 3 downstreamo2 sensors(it has 6 total). The CEL has been off for over 3 years