Engine fan randomly activates, cuts out A/C
Thread Starter
Newbie
Joined: Nov 2025
Posts: 2
Likes: 1
2020 Mercedes E450 wagon
Engine fan randomly activates, cuts out A/C
I have a 2020 E450 wagon that has the following problem:
-The engine cooling fan comes on randomly - usually at full blast, but the speed does vary at times so it's not completely binary
-The A/C cuts out when this happens
-The A/C pressure switch was replaced about a year and a half ago under prior ownership
-I replaced the coolant temp sensor
-Disconnecting the battery to reset the system made the problem go away for a few months, but it's returned
-There are no error codes stored
-The coolant temp display on the dash shows normal (in the middle)
My mechanic says his best guess is the fan assembly with the control module, but he's not 100% sure.
Since the problem is intermittent and there are no error codes stored, we're stuck unless/until he or the dealer are able to get their hands on the car right when the problem is happening.
If anyone has experience with this issue and has a solution, I'd very much appreciate the help. Thank you in advance!
-The engine cooling fan comes on randomly - usually at full blast, but the speed does vary at times so it's not completely binary
-The A/C cuts out when this happens
-The A/C pressure switch was replaced about a year and a half ago under prior ownership
-I replaced the coolant temp sensor
-Disconnecting the battery to reset the system made the problem go away for a few months, but it's returned
-There are no error codes stored
-The coolant temp display on the dash shows normal (in the middle)
My mechanic says his best guess is the fan assembly with the control module, but he's not 100% sure.
Since the problem is intermittent and there are no error codes stored, we're stuck unless/until he or the dealer are able to get their hands on the car right when the problem is happening.
If anyone has experience with this issue and has a solution, I'd very much appreciate the help. Thank you in advance!
Thread Starter
Newbie
Joined: Nov 2025
Posts: 2
Likes: 1
2020 Mercedes E450 wagon
Update
Update - I bit the bullet and replaced the fan assembly (which includes the fan control module). It's been a few weeks now and the fan has stayed off. Based on my research, the top three suspects for random engine cooling fan activation are:
1) A/C pressure sensor switch
2) Coolant temperature sensor
3) Fan control module (embedded in the fan assembly)
1) A/C pressure sensor switch
2) Coolant temperature sensor
3) Fan control module (embedded in the fan assembly)
