Hi i have a 96 civic with a 98 b18c1. I know i have 2 o2 sensors one before and one after the cat. Now, is the primary one the one before the cat. and the secondary after?? Probably by the sounds of my question but i just want to make sure. OK now my next question. On the wiring harness how do i know which of the two plugs is for the primary or for the secondary?? Are both of the plugs some where in the engine bay??

 

primary is in the header, secondary is in the cat.

the primary wiring won't reach the secondary O2 and vice versa.

Make sense?

 

no sense yet. So under the hood on the engine wiring harness are there two plugs for o2 sensors? cause i know the secondary ones plug comes out somewhere by the shifter. i just dont want to get the plugs confused. i think some of my wires have been extended also so i dont really know which is longer.