C238/E400 2017 coupe loud fan noise at idle after engine has reached running temp all of a sudden

[anyweb]

hiya,
all of a sudden my E400 C238 has started a new annoying behaviour, namely after the engine has warmed up, the front radiator fan goes FULL ON very loudly and stays on pretty much when i stop, and is very noticeable by me (and others outside the car).

I've done the obvious. looked under the bonnet to see if there's anything odd, it all looks ok, coolant level is fine and there are no warnings on the dash,
when driving and at stopped traffic the temperature of the engine remains at a constant 90c and I see no other issues aside from this, it just literally started a few days ago

any advice on what the issue could be ?

 

[Srdl]

I had the same earlier this year. Seems I got some water in the fan controller while going through a fordm which was a bit Deere than I expected, It took a couple of days but obviously dried out and has been fine since. There was someone else on here with a similar problem which occurred after driving through heavy rain. Have you been somewhere particularly wet recently?

 

[anyweb]

nope no where wet, but i have driven to the sea side and parked near the beach in the parking spaces and it was tight while i unloaded my kajak, however I can't see how that could be related.
...
I looked everywhere under the car/inside the engine bay, around the fan and cannot see any damage/sand/anything that screams out to me,

I drove the car for 3 hours in the last day (2 trips) and the issue remains, however it ****ed rain all day today.

 

[LostKiwi]

Low air con gas can cause this on some cars.

 

[anyweb]

visited my indie today and he suspected a problem with ac or the sensors straight away, we had the car on, with AC on, and then waited for the fan to roar, once it did, i powered off AC and sure enough after some minutes the roar stopped, so at least we have a direction to focus on, thanks @LostKiwi

 

[anyweb]

ok update, this is now fixed, and it was a pressure sensor causing the issue. The part number was A 211 000 0283, and it was reporting a pressure of 80psi which caused the software to think something was very wrong and forced the fan on full. After replacing the sensor with a new one from Mercedes the pressure reading is normal and the loud fan noise is gone, many thanks to my indie for not simply replacing things ad-hoc, he had the car for 2 separate days to determine the problem
first day he removed all the gas to see if any had leaked (none worth mentioning) so that ruled out a leaking condensor, and yesterday he replaced the pressure sensor which resolved the problem immediately, however the design of the sensor means it cannot be easily replaced, you need the right equipment close by or the gas will all leak out when replacing it.

anyway, I'm happy, my Indie was excellent and i'm glad he did the job and not MB.