Faulty Temperature Sensor

[cyclespeed]

Hi all, new here, but I've had my 2018 RS4 B9 for 3 years now.

For the last 2 years, it has had an intermittent fault with the cooling system. Suddenly, without warning, the water temp gauge reads wrong (usually way too low) and the fans come on full blast.
After turning car off, they continue for a few minutes.
When starting cold, the fans come on full blast immediately.
The oil temperature is always fine, correct. There doesn't seem to be any overheating issue at all.
Sometimes the fault will suddenly disappear by itself, and everything goes back to normal.
Otherwise, I have to clear the fault with an OBD reader.
So I think I need to change a temperature sensor - one OBD said it was an unreliable cylinder head sensor. Does anyone know where this is or how easy it is to get to?
Many thanks in advance!

[Jools]

There are four temp sensors on and around the engine from what I can see.
Radiator outlet coolant temperatue, G83
Engine outlet coolant temperature, G82
Engine Block temperature sender, G694
Engine coolant temp sender, G62

I'm guessing from your post that it might be G83, as if it thinks the coolant is too hot coming out of the radiators even if it isn't, it will turn the fans on.
The location is bottom right of the main radiator.

[cyclespeed]

Wow, that's really useful information thanks.

THe car is going in to a (non Audi) garage on Monday, and we will change as many sensors as necessary, hopefully testing each as they come out to find the faulty one (or more?)

I'll pass this info on the them, thanks.

[cyclespeed]

Do you by any chance know if all these 4 sensors are the same part? Or are they different?
Thanks

[Jools]

The only part number I can find is for temperature sender G694 which is 079919523J, the O ring seal for it is WHT002287B
It looks like G82, G83 & G694 are the same type of sender, but I can't be certain and are between £11 and £20 depending on manufacturer. The seals are about £2 each.

I hope this helps

[cyclespeed]

Very useful, thanks.