f12 Alarm sensor location / coding?

[sammysquid]

hi,
new here!
i've got an f12 that the alarm keeps going off - been into ista and it tells me its always the rear left ultrasound sensor thats the problem -
anyone know where this is? i can't find a guide to where this sensor lives?
and then does anyone know if you can code it out? or if i swap sensor does it need calibrating? i can't see anything