I know this sensor on a 2000 Montero Sport is right before the catalytic convertor but I've been told it's still considered downstream. Anyone know for sure?

 

Downstream, after catalyst.

 

Thank you Sebba. What I found out, after hours of looking for the two o2 sensors in the exhaust manifold, and hours of scouring the internet, is that Montero Sports that were produced early in the 2000 model year, like mine was, have only two o2 sensors, not four. So anyone going nuts, like I was, trying to figure out upstream and downstream and where these dang sensors are, hopefully this helps. There are only two, one right before the catalytic convertor, upstream and one after, downstream. Also, if you go to Autozone or Napa or any auto parts website they say to use Bosch o2 sensor with part number 13822 for the upstream sensor. The plug on the sensor will not fit into the car so you have to use a universal or I'm waiting on a Denso sensor, part #234-4645 to see if it fits. Hope this helps someone.

 

Thanks for the update!