I want to hook up my oxygen sensors on my ek hatch (OBDII). I know that one of the 2 sensors is for mixture the second efficiency of the cat converter. I found one of them in the shop, is there a difference between the 2, (cause the plug is the same)? if so, how to i know wish one I got?

 

theyre the same sensor, same wires, same everything - except the length of the wires on the 2ndary (theyre longer).
It doesnt matter which one you get...Im using a primary on my cat right now w/o issues. The wires up there are actually longer than they need to be, so you just cut the plug off the old sensor and put it on the new one so water doesnt get inside.
(2 primaries will be cheaper than one of each)