Catalytic COnverter or O2 sensor?
 

Hi all.

I have code 0420. Using the scan tool, I see that the downstream O2 sensor wildly fluctuates between 1/2 volt and nearly no volts. I understand that it should pretty much be stable at right around 1/2 volt when the engine is up to normal operating temp.

I already took the catalytic converter off and hosed it down with soap & water and all that.

Without blindly throwing parts at this problem, how can I find out if it is the O2 sensor or the catalytic converter itself?

The cat has about 165,000 miles on it and it had a terribly dirty intake air filter and throttle body. The ECR passage was pretty clogged, too. I cleaned that stuff up.

Thanks!

PS - Car is a 1998 Accord EX 2.3 liter VTEC 4-cyl.

Good video from ericthecarguy:

Ya, I'm guessing its the converter and not the O2 sensor.