Radiator fan always on

[triplecee]

Hi fellow benz owners! ive scoured these forums looking for similar issues but havent found any posts which address my issue. when i start the car, the rad fan turns on and stays on until the car is shut off. ive had 2 malfunction messages " washer low" , and " coolant level low". ive checked both and the levels are fine. the engine temp had never moved above 90 degrees celsius so i know the motor is not overheating. the check engine light has come on and my mechanic told me its due to an altitude sensor. im assuming the fan is turning on due to the low coolant warning but after resetting the malfunction warnings the fan still starts. bieng a benz noob and not a mechanic, can anyone shed some light on my situation before i shell out cash to a mechanic? thx!

[Whosdis]

The only thing that crosses my mind are the coolant level sensor is still bad, or a coolant temp. sensor is bad. Most of the time a coolant fan stays on is because it doesn't know how hot the engine is and it doesn't want the engine to overheat.

[triplecee]

thats what i was thinking. would the fan turn on due to low coolant as well as high temp? i know my motor isnt running hot, but does that read from a different sensor than the coolant temp? i think ill start with the coolant level sensor as ive had the low coolant malfunction turn up on my instrument display, if that works then ill try coolant temp sensor. thx for the response!

[jerk_chicken]

In my case, I saw my fan going haywire when I had low alternator output, even when it was just barely high enough to not initiate a warning. Several times, it followed all of my warnings going haywire. Alternator is fine now and the fan doesn't go haywire.