Do are cars have one before and after the cat?



Thanks

 

They just have one sensor, on the drivers side exhaust manifold right before it goes into the Y-pipe. Thats where mine used to be rather than install a bung into my headers, we put it downstream in the pipe that is now where the cat used to be. I had concerns about it taking longer to warm up that far downstream but it seems to have made no difference at all.