Does the oem 2001 1.7 exhaust manifold oem have the cat built to it?
Reason fixing gf car having it on the lift I noticed no cat, while replacing oil pan gasket. We are getting O2 codes for sensor 2 but previous owner seemed to do a modification. Elbow like attachment to aftermarket header to O2 sensor.

 

The EX does not have a cat on the manifold, it's on the bottom of the car after and is actually part of the B-Pipe A-Pipe. The LX/DX engines however do have the cat on the manifold.

Look for the engine code

D17A1 = LX/DX
D17A2 = EX

The elbow 02 modification is to fool the ECU into thinking the catalytic converter is present when it is in fact not. If you're throwing O2 sensor codes for bank 2, the problem is likely to be the O2 sensor itself if that elbow is present. Now, if you remove the elbow, you'll get a P0420 Catalyst Efficiency low code along with your O2 sensor code.

 

I had that elbow on my aftermarket sensor, it only works for so long before the computer figures out there is no cat. More than likely the owner went catless. Your best bet is to buy a new manifold w/cat (magnaflow makes cheap ones they have them on amazon and ebay) and replace your secondary 02 sensor (rockauto dot com) as that one is probably fucked after being run with no cat for a while. If you have an EX then it's an entirely different story. Either way sounds like your are going to need a new cat and an o2 sensor. Luckily secondary 02 sensors for 2001s are cheap. Not wideband like 04/05 civics.