i thought it was a lambda sensor
if you can take out your one 22mm spanner and take the part no off it i'll be able to help with a price, there will be 2 numbers a reno one and a bosch one just jot down both if it matches one i've got in they retail for £69 + vat you can have it for £50 all in the bosch ones are £88 + and genuine are £96+ (all approx by the way(the gsf one is probably a wire in jobbie not very good at all, the more joins in a wire the more the resistance increases therefore signal is altered these things operate between 0 & 500 millivolts (ish)
I always thought it was the Lambada sensor lol