right just went for a litte drive.. and the light neva came on then it did after like 10 minutes .. then went back off.. then back on .. back off.. you get the idea

its not consitantly on.. and looking at the gunk in my bottle i would say rich is right and better of getting a new bottle ..
i will unplug the sensor tomorow too see if that makes any difference
Can you not clean the metal prongs? this worked on my Seat 1.8T. Bottle is only £15 but every little helps!
Have you reset the engine light to see if it comes back?
You can indeed 
how do i reset the engine light?? iv put it on vag com no fault codes came up
