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Aux fans stay on

2K views 10 replies 4 participants last post by  poddack 
#1 ·
So my aux fans were acting up a few months ago and i noticed that the belt had slipped off and tangled causing the fans not to run. Put the belt back on then everything went well.
Today drove back from work parked the car but the fans were still running at high speed so i figured i let it be (thought it was normal) since some cars do that. Well after 5 min the fans still going full speed with the car off. Checked the main big fuse in the bay and still good, removed the fuse and the fans stopped. Popped it back in and fans went back to full speed again, btw all these is happening with the car completly off, not even a key in the ignition. So i removed the fuse let the car sit for an 1 or so then poppd it back in, this time all was good, BUT as soon as i slammed the hood shut bam the fans started again..what a hell could this be? I hope its just the fan modul at this point and not some electrical gremlin. Whats shocking is that all these things are happening with the car off.
Whats do you guys think, shoudld i go and order a new FCM or is there any other fuses/relays i should check?
Is ther a way to get to the fcm without removing the bumper and headlight?

T
 
#4 ·
On my C280 12v is on pin 1 on the fan module and is hot all the time. If fan module shorts out the fans could run even with car off. The climate control module supplies control voltage to pin 5 and goes to 0v with car off, which should kill the fans. Not sure if your car is the same, but probably similar. Good luck!
 
#6 ·
It is likely the fan control module. The climate control module goes inactive when the car is shutdown on my car. Of course, your car is a different model and it could have a different wiring set up, but if it is the same the ccu supplies control voltage to pin 5 which connects pin 1 to pins 2 & 3. You need a wiring diagram of your car to see how it works and what is wrong.
 
#8 ·
Thanks for some of the feedback guys. So yesterday I got to the FCM disconnected the plug and did some measurements with voltage meter. as Franklyspeaking mentioned the power to the connector is always 12 volt even with the ignition off. I also checked the signal side but that showed 0, which makes sense since the car was off. So it seems like the FCM does the voltage regulation (as expected). Next step is to get a new one and swap it, that will be the "real test" I guess. To get to the FCM it seems pretty straight forward from the bottom, just need the driver side fog light out of the way, this makes me relieved as I really don't want to remove the bumper and headlight.
@fabbrisd1 I don't think the MAF sensor is bad, because bad MAF sensors cause huge drivability issues. The car drives fine and there is no fuel consumption issues. I hope its not a ECM issue since I don't get any other faults. I would think a MAF or ECM issue would cause Christmas lights on my cluster and other drivability issues. If it is the ECM than bye bye aux fans OR I will put a kill switch for just the fans :)
 
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