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Steve
Steve, BMW Expert
Category: BMW
Satisfied Customers: 23882
Experience:  BMW Expert
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hi there I own a 12 year old 5 series BMW (2002)520i and am

Resolved Question:

hi there I own a 12 year old 5 series BMW (2002)520i and am getting mix advise about the AUX Fan/AC Fan, its running so fast its like a jet engine ! First I was told the fan is fine and I need a Auto electrician to correct the voltage going to the fan, the auto electrician says theres no such thing, and that he can do a diagnosis to check if the fan is faulty but this can be costly. I don't want to spend monie on a new fan if the fan is fine. the fan works as soon as I turn on the key but it gets so noisey after 30 sec, the fan is spinning so fast causing this heavy noise.
I have recently replaced a E39 resistor coz it was faulty and was draining my battery life, I was so happy and everything seemed fine, after a few weeks I got this problem. could this be related? do I need to reset something? officially the ECU is sending the wrong signal to the fan, its spinning way too fast.
Could this be the Aux Fan power connector and temp switch?
Cant wait for a proper BMW specialists answer.
Submitted: 2 years ago.
Category: BMW
Expert:  Steve replied 2 years ago.

I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.

the fan runs based on coolant temperature and pressure in the ac system then based on a variable speed controller internal to the fan.

it has constant voltage so correcting voltage wont help, and this has nothing to do with the resistor you replaced.

most likely one of the two sensors (pressure and temp) is sending the wrong signal causing the car's computer to trigger high speed fan running all of the time, however, there is a slight chance the issue is also internal to the fan's speed controller.

the cause can be verified with a factory BMW scan tool which can monitor all inputs and outputs from all systems. I assume this this testing has not been carried out.

if you would like to avoid guesswork on this, you will need to invest in this type of diagnostic

Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.

Customer: replied 2 years ago.

Hi steve can I sort this out myself?? can I repair the two sensors (pressure and Temp)? when can I find the speed controller?

Expert:  Steve replied 2 years ago.

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you

if you want to avoid guesswork, the proper diagnostics with proper equipment must first be carried out

if you want to start replacing sensors without first verifying, you could potentially do this yourself, but I can't say for sure as I do not know your abilities and equipmpent level

the speed controller is internal to the fan, it is not something you can find seperately/

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you

Customer: replied 2 years ago.

Hi steve sorry about the wait, ok where are these sensors?

Expert:  Steve replied 2 years ago.

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you

the temp sensors is in the radiator/outlet hose

the pressure sesnsor is at the drying container of the AC system

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you

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