liebherr refrigerator not defrosting

I have a liebherr c1601refrigerator/freezer (Service number 0916375-00) that no longer self defrosts in the refrigerator, the problem was intermittent for about year but now it has completely stopped defrosting. I understand that it most likely needs a new evaporator sensor, could someone confirm that the evaporator sensor is most likely the problem. Many thanks.