It literally pops off. But remove the washer jet covers first.
I to found out the hard way and one snapped off.
Pull it out with your fingers and then lift the tab that holds it in place.
The oem sensor was for my impreza at £306.
I cleaned the inlet on my impreza, and levorg, and my impreza was clean before I started.
My levorg was like a dirty diesel, and although it felt much more responsive after cleaning, it didnt improve mpg...
If Esso is better than momentum, I'll get that as it's the same price where I am.
Vpower however, is about 10p more.
I read an interesting thread on scoobynet.com about o2 / lamba sensors clog up with carbon build up and all they need was a blow lamp to make it red hot to burn the carbon away...
Im just intrigued, as the Tr690 isnt avaliable here, unless I import from Japan, and then there's the language barrier.
There is nothing wrong with mine, but a spare could bs handy.