I have a 97 Civic HX thats throwing the code P0420. After doing research I figure the cat is bad on the car being that it has 186,xxx miles on it.

My questions is the OEM cats are so expensive, is there after market ones that will work the same. Or can you just put a header on the car and it get rid of the CEL?

 

only way your car throws a p420.

intake manifold leak
cat bad
o2 bad

header is not one of these unless your exhaust manifold has a crack

 

The O2 is good, it was just replaced. And the header would get rid of the cat(if it's bad) because the cat is bolted directly to the exhaust manifold. It's not under neath the car like most cats are.

 

which means you have a 5 wire o2. which o2 was replaced bc you have two of them? new doesnt mean good.

if you delete the cat (i.e. header) you will still have the code.

you really have to scan the o2's and see whats going on there. a typical scanner will have a hard time seeing the "switching" effect due to you having such a fast switching 5 wire 02.

who did the new o2 and whcih one? why did you replace the o2?

 

The O2 was replaced by a mechanic locally right after I bought the car(3 months ago) and it was bank 1. So it was before the cat, I didn't know it had one after the cat, my older honda's didn't. The reason it was replaced was it was throwing a CEL. After it was replaced it went away.

 

A 97 Civic has two O2 sensors, one before and one after the cat. A bad O2 sensor will not generally cause P0420 unless an O2 sensor code is thrown. Therefore, you either have an exhaust leak or the cat is bad. The latter is most common.