Typically P0420, "Catalyst System Efficiency Below Threshold"

You can buy a little electronic device called an "O2 Simulator" that can be wired in to fool the computer, allowing you to run a test pipe.

 

Yeah, what he said^^

but its not worth it... stop looking for places to spend money and 'upgrade' believe me, Im speaking from experience. Figure out where you are going with the car before buying things like this.

 

i have a hight flow cat "test pipe" on my civic and it dosent through no codes or anything and it dosen't waste gas ither it dose not change a thing, if you change your stock to aftermarket, it is better cause you are letting the car breath more so witch means you car will run better and get better gas millage cause i did it to my 95 civic 4dr ex so i know first hand it dose not change anything

 

No shit, you have an OBD-I computer in your car. Only 96+ OBD-II compliant Hondas throw catalyst problem codes. The person asking owns a '97.

 

Thank god Im not the only insane, illiterate on here! Haha Kai, thanks for covering.

 

hey guys thanks for all the suggestions. This is what i plan on doing to the car, i'm going to start making a homemade turbo kit, and in a couple of months when i have all the parts put it on. But right now i have like 105k miles on it and i was thinking that it might be time for a new cat., so i was either going to buy a high flow cat. or a test pipe. The test pipe i was looking at as a bungle for the o2 sensor. So with that said test pipe or high flow cat?

 

It doesn't make a difference. Even if the O2 sensor is mounted in the test pipe, it will throw the check engine light because the computer is seeing bad readings (due to the lack of a catalyst.)

 

Read above.

Dont do anything. If there is no CEL right now, then your cat if fine. Leave it alone and save the $100 or so.

 

Dont change it untill you get the turbo. Then it is up to you which one, both will likely throw a CE light. Both would definitely help the power w/turbo. If you go with a test pipe, you will always need a hook up from someone when it comes inspection time. Sometimes that can be a pain in the arse to find. Not to mention expensive.
I'm not sure about on Hondas, but on my old Eclipse. I just wired a resistor in line with the rear O2 sensor, and by by CE light. ($.50) Same thing on my WRX. The WRX has 3 cats, talk about freeing up some breathing room for the turbo. May they both rest in piece...s
Watch for the black soot sticking to the car around the tail pipes too.

 

Sorry I should check the dates before chiming in on some of these threads...