check the 2 coolant flanges on the head for a black collar sensor with a red/yellow wire. could be 1 pi or 2 pin depending on the year. can be hidden in the bottom of the front flange so is hard to spot.
049 919 501 - 1 pin sensor, black - 27.50+VAT
251 919 501 D - 2 pin sensor, black - 21.36+VAT