HEY TECHERS, I JUST GOT A 98 EX CIVIC, I WAS WONDERING WERE I CAN LOCATE THE REAR 02 SENSOR, THE DOWN STREAM ONE ON THE CAT? .. OR WHICH ONE IT IS....

 

After the cat

 

THe seconday O2 sesor is in the catalytic converter. There are 2 02 sensors. The primary can easily be seen under the hood on the exhaust manifold. The other is at the bottom of the cat and can be seen too. It points toward the drivers side at the bottom of the caonverter. Your cat converter hangs right off of your exhaust manifold collector flange. Very easy to change from under the car.