Hi everyone, 

 

I've had this problem for quite a while now and I can't find any solution to it online and no where. I have a 2013 Fiesta SE, everything works completely fine with it except that the engine cooling fan doesn't turn on when raining or getting wet (it being washing the car, etc). It doesn't happens very often just when getting large amounts of water. 

At first I thought it could be a problem with the Ambient Air Temperature sensor since when this happens in my dashboard temperatures below 0 appear (see picture),

but here is the thing, my dashboard never shows any outside temperature it only does when it rains and I get the problem. To the point that I dont even have the AAT sensor installed lol with or without the sensor it always appears "--" where outside temperature should be showing. I once replaced this sensor but it never showed any temperature and it fixed my issue for a while! But it is happening again, with or without the AAT sensor.

I've checked this sensor plot and the cables and everything seems to be fine. Also the AC is not turning on neither, wich at first I thought was my only problem but then I realized that the engine cooling fan its not turning on aswell. I thought it was the AAT sensor because of the below 0 temperature thing, but maybe it could be another thing? I don't know Im not a mechanic nor know a lot about cars, and because it is such a particular problem that happens when it rains I can't find anyone with the same or similar problem online. Funny thing is everything goes back to normal when it dries out. 

If someone could help me with this I will really appreciate it... Thank you in advance!

(PD: Idk if it should be important that the AAT I once replaced was a replacement and not an original part, bare with me the original one was a little expensive and I didn't want to expend more money while having the possibility of not fixing the problem... which... kinda happened with the replacement...)

There's a lot going on in your posting and it is confusing. In wet weather, I wouldn't expect thecar to need its cooling fan.  Do you mean it randomly comes on? You get odd dash messages when the fault occurs. I think the aircon not cutting in could be the result of the fan not running, or it could be the other way round. You won't know where to look under the bonnet, but look anyway for any chafed wires. Be thorough because if you don't find any,  there is no way you'will fix this on your own.

5 hours ago, anon said:

There's a lot going on in your posting and it is confusing. In wet weather, I wouldn't expect thecar to need its cooling fan.  Do you mean it randomly comes on? You get odd dash messages when the fault occurs. I think the aircon not cutting in could be the result of the fan not running, or it could be the other way round. You won't know where to look under the bonnet, but look anyway for any chafed wires. Be thorough because if you don't find any,  there is no way you'will fix this on your own.

Hi! I am sorry my post is confusing its my first time posting and honestly I don't really know how to put this problem into words lol... what I meant is everytime there is rain or my car gets large amounts of water in it (for example washing it) the fan doesn't turns on. I expected my car to need the cooling fan since I live in a hot weather country, though I've never experienced engine overheating when this happens, I did noticed that coolant rises up and then it could get leaked out if driving for a while. Maybe the car doesn't need the fan when raining (which would make sense why it turns it off in the first place) but the AC also cuts off (it just blows air not cold air)... this and the coolant rise situation is why I think it is a problem. And yes when this happens I do get that message in my dashboard as if there were crazy cold temperatures (see the image).

Your posts get more confusing and I cannot understand the problem. I think you need to discuss this with a competent garage. We cannot do guesswork without a clear understanding of the problem 

Check the plug to the fan and the resistor or module (both types fitted to these).  I suspect one will be corroded and the damp is the final straw to break the connection.

I had a fault like this on a Mk6 a few years ago.  Wouldn't start after being washed, chucked so many fault codes it could only have been a wiring issue, but nowhere really pinpointed to start looking.  It was fine the next day once it had dried out, but I was very careful washing it after that.

On 8/18/2025 at 4:35 AM, TomsFocus said:

Check the plug to the fan and the resistor or module (both types fitted to these).  I suspect one will be corroded and the damp is the final straw to break the connection.

I had a fault like this on a Mk6 a few years ago.  Wouldn't start after being washed, chucked so many fault codes it could only have been a wiring issue, but nowhere really pinpointed to start looking.  It was fine the next day once it had dried out, but I was very careful washing it after that.

Thank you! I'll try to look into that, I've looked into the AAT cables and everything seems to be fine, maybe I am looking in the wrong place.