I know there have been similar topics but I have not found one that seems to go as far as the issue I have. ANY help would be greatly appreciated.
Last November, my 2018 s5 gave the low coolant warning but had full coolant. I thought reservoir senor, changed it no luck. Then I leaned of the switching valve solenoid, changed that and problem solved. Until a few weeks ago I got the same warning. So I gave in and took it to the dealer.
First tech they said was change the reservoir and the harness that connects to the coolant level sensor.
I told them to please look further as I have just changed the reservoir and switching valve with an OEM parts. The service advisor put me on the phone with the lead tech and I expressed my concerns about the knowen issues and service bulletins regarding the coolant pump and thermostat. He said to look into the coolant pump and t stat did not make much sense to him and after putting a new reservoir on the car just to check he found that the resevoir was not the issue nor was the harness.
Next after speaking with Audi engineers or whoever techs call for help at Audi, he recommended the comfort convince module. He stated its believed the module is sending a bad signal to the dashboard, $1800 job and if it did not work I was SOL on that money and they move on to the next thing. So I decided to I would rather gamble and change the coolant pump and T stat and the 2nd switching valve that is under the t stat while I had everything apart. I figured worse case I spend money and time on parts that I would possible need soon and hopefully fix my warning light. Well I changed it all tested the cooling system for leaks and used a vacuum system to fill it with coolant so I would reduce the risk of air pockets and No LUCK

Anyone have any idea what else could be the cause? Maybe it is the module? Has anyone had issues with with comfort module like this???
Again any ideas are appreciated. Thanks