How to replace the coolant temperature sensor on an Audi 80?

My check engine light came on and I suspect it's because of a faulty coolant temperature sensor. How do I replace it on my Audi 80?

First, locate the sensor which is usually near the thermostat housing. Then disconnect the electrical connector and simply remove and replace the sensor.

Before replacing the sensor, check if the wiring and connector are damaged. If so, fix those issues first as they could also cause issues with the sensor.

Make sure to drain the coolant before removing the sensor to avoid a mess. It's also a good idea to replace the o-ring while you're at it.