Neff fridge freezer K9724X7GB/02 FD9206 control erratic

My integrated Neff FF K9724X7GB/02 – FD9206 controls erratically and sometimes alarms. It is not frosted and I have changed the control module and the freezer air temp thermistor (B3 on the circuit diagram). No improvement. I think it may be one of the other two thermistors in the evaporator (B4 and B5) but I am not sure of their location and if they can be replaced. On the Neff parts drawing I can see item 0118 which appears to be a sensor but it is not listed in the parts list. Any assistance on the function of the sensors and replaceability would be appreciated.