Bosch KGU31165gb/01 freezing food in fridge

Hi folks Refridgeration not my forte but here goes,All in the fridge the thing never seems to switch off and the fan doesn’t come on according to the customer. The temp setting displays are lit no obvious build up of ice,so was wondering if the sensors or PCB control the temp and fan,looks like the probe cant tell how cold it is and wont switch off the compressor or the board cant tell what to do???????????