The tailgate on my XF 2013 Sporting brake has stopped working. I get a double blip on locking the car. I can hear the motor whir and then the tailgate is pulled in on the soft close. I then hear another whir and it doesn't allow me to lock it. If I push my knee on the curved part of the tailgate at the bottom it then flashes the indicators and allows me to lock the car. This made me think it was just an alignment issue so I tried moving the whole tailgate and the boot floor lock under the chrome trim and it has made no difference. Where is the sensor in the tailgate so that it knows it is shut ? Is there something in the struts ?