There is, what looks like a full VAG engine fault codes on Briskoda - in the VAG COM and Diagnostics section of the forum - you can view this without joining (I think). I'd think that its normally the heater circuit on sensor 1 (sensor nearest the manifold) that seems to fail on these cars, so I'd expect them to tell you that they need to replace that sensor. As time goes on, if this is the current fault, then it will appear more often and finally stay on all the time when the sensor has become completely u/s.