Hey guys, haven't posted here before but I've been posting on civic forums for quite awhile. I'll get right to the point, I need to take an emissions test in the next couple of weeks, and I have a P0420 code that I can't seem to get rid of. I've replaced the catalytic converter already, and I'm thinking of switching out the o2 sensors but I want to make sure that's the logical next step. Also the idle on my car (2000 civic so with 120K miles or so), is a little jumpy. I've checked for exhaust leaks and I can't find any, so I'd appreciate the help. Thanks in advance guys.

 

Oh and also, I've reset the code a few times and it doesn't come back on until after a few days of driving or so. It doesn't seem to be effecting drivability at all besides the idle (I'm not sure if this is a related issue or not), so it's just kind of a nagging problem that needs to be resolved because it won't pass emissions with the code. Thanks again.

 

all sensors and plugs correctly in place? the jumping idle is most likely from a vacuum leak or a IAC Valve. Im not sure about the code...

 

Are your sensors aftermarket or OEM o2 sensors? Before throwing parts you should look at the o2 patterns with a scan tool and see if the sensors are giving correct readings? Where did you get the cat from? OEM? Answer some of these questions, and PM me and I can try and point you in the right direction!

 

The sensors are OEM, but they are pretty old. Not sure when they were replaced last but it's been at least a few years, which is one of the reasons I'm thinking they could be the root of the issue since the cat is replaced. The cat is an OEM replacement from Bosal...I wanted a Honda one but the dealer quoted me like a million dollars so I got one from Bosal. They seem to be a pretty reputable company, they're pretty popular in the subaru world for exhaust manifolds and exhausts. What kind of scan tool would I need to check the sensors? Thanks for your help bro.

 

ttt