What is this sensor..

Coolant temp.  Can also be called head temp on earlier models.  It is temp of the coolant flowing through cylinder heads.

The newer style heads on cylinders 2 & 3 (suffix -01 engines) have the temperature sensor mounted on top of the head, and in this case the sensor is flooded with coolant so is considered a coolant temperature sensor.  The older style heads have the sensor mounted under the cylinder, and in this case the sensor is not in contact with the coolant so is considered a CHT sensor.  Here is a link to the Rotax video covering this.

https://www.rotax-owner.com/en/videos-topmenu/rotax-minute/448-newcylheads

Makes sense.

thanks guys.