I changed my cat out for a high flow one about 4-5 months ago now I am getting a code p0420 catalyst efficiency below threshold (bank1). Someone said it might just be my oxygen sensor could it be? thanks for any help guys.

A. Gokool

 

It could be an O2 sensor, or the cat itself could be bad.

It wasn't one of these style HFCs, was it? Those are nothing more than resonated test pipes...

 

best way to tell is to use consult and graph both of the o2 sensors, that will usually tell you if the Cat is bad or is the o2 sensor is bad. the bad thing is you would have to goto nissan or something like that to communicate with your ECU that has the ability to data monitor .

 

well It wasn't one of those e-bay cats, my buddy owns a muffler shop and did it for me. will this damage anything on my car?

 

I just looked under the car and it looks something like that one in the pic...

 

Did you have a light before the new stuff.?

 

I had this code intermittently while the car was bone stock (minus the intake). It ended up being one of my downstream O2 sensors. It never hurts to replace those if they haven't ever been done.

 

NO i didnt. but it goes on and off.. Like if I run the car really hard it wold cut off and say off for a day or 2 then pop back on and the car starts to drink gas....

 

You need to get an o2 simulator for your downstream sensor.

 

Heres your easiest way to tell. Put back your old cat if no CEL comes on, then its the test pipe/resonator. If CEL still comes on its your sensor. I bought one of these but decided not to put it on, maybe Ill try it out at the track(the supposed 5-10hp gains they advertise).

 

whatsa 02 simulator?

 

oh the power is there with the test pipe. **** moves...

 

It's a 3 wire circuit board that will tell the computer that everything is ok. The o2 sensor before the cat is for the air/fuel ratio, the sensor after the cat measures the amount of oxygen that passes through the cat. If the rear sensor is reading the same amount as the front sensor, then it throws a code because the cat is not doing its job.

 

I see I see and where can i get one of these?

 

O2simulator.com 40 bucks shipped.

 

where could someone get a "decent" test pipe at ? if thats even possible..... flanged 2.5 FTW????? i would hate to get one off ebay.

 

thanks..



Thanks for all your help guys..