I've had this issue for a while now, and it has gotten worse and worse and is now getting too annoying.
When i start the car, the FIS will beep three times and show the red coolant error light. After driving a few hundred meters it will go off and work normal again. If it's around 0c, it will stay on for like 1km.
I noticed this problem first in the winter, when i had to start the car in about -10 degrees without heating, but worked well in -5 or warmer. Now that the weather is getting warmer the critical point has moved warmer, and i'm getting the same beeping now in +20. Will not stay on for very long, but it shouldn't be on at all.
Vag-Com gives me this fault code:
16500 - Engine Coolant Temp. Sensor (G62): Implausible Signal
P0116 - 35-10 - - - Intermittent
I obviously thought it would be the temp. sensor on the drivers side of the cylinder head, changed it but didn't help at all.
I could imagine the fault being inside the speedometer, as i have this brake light issue too with autocheck, which i'm pretty sure is an issue with the speedo, but it doesn't explain to me why it goes away after the coolant gets a little warmer.