Identify temperature sensor?

I have a temperature sensor on a board which measures room temperature. I am convinced that the sensor is faulty, so I need to identify it so that I can replace it.

The sensor has two pins and is square in profile, about 3mm x 3mm x 2mm, with no identification markings, although there are two white patches on the top, and a semi-circular marking on one face, but that may be just chance. There is some sort of white sleeve on the pins.

How am I to go about getting the correct replacement? I've got a very good multi-meter. Thanks.

I didn't find it.
Since it has only two wires, it could be a NTC or PTC. Those are availabe in a TO-92.
If you remove it from the board you can measure the resistance with different temperatures, to determine if is a simple NTC or PTC.

Or, with the R2 marked on the circuit board, it could be a thermistor. Have you tried measuring the resistance between the two leads? Take a look and see if the device is "in circuit' or not. Probably start with your ohmmeter in the RX100 scale. Just squeeze it between your fingers and see if the resistance changes. If it changes, I'd look for a different problem.