Aux Fan Always Running

J

jampudding

Member
Hello All,

Car - E85 3.0L

My Aux Fan starts running about 10 secs after I start the car and continues until I turn the car off, it is running at full tilt. From research I assume it's one of 3 things probably more:

1. Relay
2. Coolant Temp Sensor
3. Coolant problem - possible air bubbles in coolant therefore needs draining and refilling possibly.

Now I know where the relay is and where the coolant drain is - but can somebody tell me where the temp sensor for the Aux Fan is? Just want to know where everything is before I start working on things.
Lastly please tell me if I am barking up the wrong tree!!

Kind Regards
 
Fans always running whit aircon on, make sure it's off before panicking.

Sent from my Xperia Arc S using Tapatalk 4 Beta
 
The temp sensor is on the radiator outlet. The online WDS usually has pictures where components are located, but not in this case. The fan is controlled by the DME so the engine coolant temperature is factored in along with outlet temp. On N52s the ECT sensor is on the thermostat housing. On M54s it's on the bottom left of the block, about in the middle of the block length.
 
Marius said:
Fans always running whit aircon on, make sure it's off before panicking.

Sent from my Xperia Arc S using Tapatalk 4 Beta
Click to expand...

^^^^What he said. In the current weather we are having with aircon on my auxiliary fan is also running constantly. Sitting stationary it seems louder than the engine. Switch the aircon off and it stops immediately - at least I find it does. If the aux fan is also linked to coolant temperature as well as bcworkz says, then that also will be a factor in this heat
 
Thanks all for the replies.

Although the weather has been very hot I have not been using my A/C, the fan is just running.
bcworkz - I had a look at the WDS wiring just to research the AUX fan relay but I can't understand which one it is, do you know which it is or if it is marked in the car? I have seen it suggested that as a test of the relay it can be swapped with the fog light relay - or presumably any relay which is the same.
Also if I understand you correctly there are 2 sensors:
coolant sensor - on the radiator outlet
engine coolant sensor - on the left side of the engine block halfway down the block
Is that correct?

thanks
 
Yes, there are two sensors. On further thought, I may have been confused about which sensors effect what. Both sensors factor into the DME controlled thermostat. It's not clear what factors onto the fan operation, though it's certainly the radiator outlet. Whether the ECT factors in or not is not clear in the resources I have.

As for the fan relay, it appears to be mounted on the fan motor. I've no idea if another relay can be substituted as a test. I suspect not, as the fan's speed is controlled by a square wave signal from the DME, so it is more than a dumb relay, the fan speed is proportional to the signal wave length.
 
I managed to disconnect the electrical wires to the coolant temp sensor. The electric/aux fan did not run automatically as it did before and at full throttle. Interestingly when I stopped after a 20 min drive the fan ran but at a very low setting - and I did not have the AC running. This suggests that perhaps the engine coolant sensor does have an input to the electric/aux fan.
Irritatingly the passenger airbag light came on. I assume this was because I disconnected the wire without disconnecting the battery - I'm hoping!! Now I 'll buy a new sensor and see if it makes a difference.
 
Interesting. Sounds about right. Replacing the sensor seems like a good bet. I can't imagine how this would effect the airbag light, but it is too much of a coincidence, maybe I need a better imagination. I'm surprised the CEL didn't go on, perhaps it takes a few drive cycles with the same condition to trigger it. I hope this solves it!
 
As an update had the colant temp sensor and lower hose that it attaches to changed and no AUX fan running. The Airbag light I just had cleared at my MOT garage. so for a check to this problem it's worth disconnecting the wires to the coolant temp sensor. The sensor is just £21 from BMW.
 
Currently having a similar issue myself,

I have noticed that the fan has began to kick in at some point during my morning drive and not turn off until the car is switched off. Heaters are on and hot, but the fan remains on even when the heaters are then switched off.

It doesn't happen every day, maybe twice a week.

Aiming to get the code reader out this weekend
 
Wrighty said:
Currently having a similar issue myself,

I have noticed that the fan has began to kick in at some point during my morning drive and not turn off until the car is switched off. Heaters are on and hot, but the fan remains on even when the heaters are then switched off.

It doesn't happen every day, maybe twice a week.

Aiming to get the code reader out this weekend
Click to expand...

Is yours a repeat of the previous post when the fan is running with the aircon switched on?
Is your car an si with the n52 engine and how many miles has it covered? Has it ever had the electronic water pump changed?
When the pump on my si was on the way out it was causing the fan to run at odd times including cold starts :?
Rob
 
Smartbear said:
Wrighty said:
Currently having a similar issue myself,

I have noticed that the fan has began to kick in at some point during my morning drive and not turn off until the car is switched off. Heaters are on and hot, but the fan remains on even when the heaters are then switched off.

It doesn't happen every day, maybe twice a week.

Aiming to get the code reader out this weekend
Click to expand...

Is yours a repeat of the previous post when the fan is running with the aircon switched on?
Is your car an si with the n52 engine and how many miles has it covered? Has it ever had the electronic water pump changed?
When the pump on my si was on the way out it was causing the fan to run at odd times including cold starts :?
Rob
Click to expand...

Similar issue Rob but not the same no. I believe the fan comes on at some point when the heaters are on. Then only goes off when I turn the car off. This doesn't happen every day which is the unusual thing to me.
M54 engine, SE I believe, water pump changed around 12 months ago
Thanks
 
Possibly the coolant temp sensor on the way out? There's 2 sensors, one near the block that is linked to the gauge on the dash, and one on the radiator return pipe which isn't shown. If the ECU can't read what temp the coolant returning from the rad is, it runs in failsafe mode with the fan at 100%.
 
Codes read, "2790 Radiator outlet temperature" looks to be the likely culprit :thumbsup: Will look into getting it replaced.

Plenty of instrument cluster, dials, CAN related codes too which was unexpected
 
Wrighty said:
Codes read, "2790 Radiator outlet temperature" looks to be the likely culprit :thumbsup: Will look into getting it replaced.

Plenty of instrument cluster, dials, CAN related codes too which was unexpected
Click to expand...

Simple fix then. From experience the third party ones are junk, a new BMW one is about £20.
 
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