Hi,

I have been googling it up like a crazy person lately trying to find where the secondary O2 sensor on a 99 Civic Si plugs into?

I cant find anything in the engine harness, and I have yet to find anything in the cabin harness?

Any help would be greatly appreciated!

 

There's a hole in the floorplate directly above the cat. The plug should be right inside there. you access it from underneath the car.