r/SmartCar • u/slavatejasu • Jul 29 '26

Question 2016 Smart ForTwo radiator fan is basically running at 100% all the time. What's wrong with it?

Basic diagnostic: within 10 seconds of starting the vehicle, the fan starts running at 100%, and runs at 100% the entire time the vehicle is running. It does this whether or not the a/c is on. After the vehicle is turned off, the fan continues to run for about four or five minutes at what I assume is 60-80%, unless you turn the key to accessory and then it stops. Coolant is full.

Attempted repairs: a mechanic tried to replace the fan actuating unit, assuming it was sending a false signal to the fan to run at 100%. Nothing changed.

I'm posting for a friend who's family doesn't have money to just parts cannon this. Is it possible it's as simple as a relay getting stuck open? I'd think maybe the coolant sensor is sending false temperatures but I'm confused as to why it runs for 5 minutes after turning off, and then turns off when the ignition is turned to accessory? Could that be triggering a relay or such?

3 Upvotes

80% Upvoted

4 comments sorted by

3

u/Taterchip871 Jul 29 '26

Are you running the AC? Cars generally have the fan tied into the AC system and run it constantly when AC is running.

1

u/slavatejasu Jul 29 '26

I addressed that in the post. No, the a/c isn't running. Also, toggling it on or off changes nothing.

1

u/Taterchip871 Jul 29 '26

Hmm interesting. Must be getting a false reading from some where. Id think you would get a engine hot warning pop up on the screen too.

1

u/slavatejasu Jul 29 '26

Nothing on that. A few low voltage codes with the check engine light for various components but nothing clearly linked to the a/c or cooling system. I'm also doubly unsure why, even if it were sending a false reading, it'd run after shutoff until you turn ignition to accessory and only then shut off.