P0240 2nd cat Options

[xrav22]

Hey there I have been reserching this code (p0240)for a while now and now need some help.

It states my 97 GT has a weak catalytic converter #2. Now since this started I am only getting 275 to the tankfull. Before I was getting well over 300.

I gave a complete tune up. I keep shutting the engine light off but it keeps popping on every tankfull or so. When I got a smog I replaced the two 02 sensors by the exaust manifold. The guy at smog said that the top sensor was for fuel ratio and I didn't need to replace it. I replaced both anyways.

I thought both were 02 sensors. So if my problem is cat #2 I am assuming there is another cat halfway back on the car. Before I go crawling under there does anyone know if there is another sensor down there and has anyone replaced that cat with another if so what brand is ok.

I read aftermarket cats don't want to work. Anyways I cant find a pdf or anything that shows that part of the exaust.

Thanks in advance.