2002 E39 530i Auxiliary stuck on high, even with car off! (ac works fine)

[ThatSandMan]

Hi this is my first time on the bimmer forums so i apologize for any conventions i mess up.

I recently bought a 2002 bmw e39 530i the previous owners parked the car and neglected it despite it working fine because they got and 540. It sat for 2 years I recently went over swapped the gas and battery and used a little starting fluid to get it running, I then purchased it from the owners for a deal! The car runs great I have been driving it for the past few days and have not had any issues, but today at the post office the auxiliary fan kicked on high and will not shut off even if the key is removed. The only way i can get the fan to shut off is if i remove the battery terminals, I did some research and saw that some others had this issue and it turned out to be there blower motor resistor (FSR?) but my air conditioning works just fine and my outside temp display on the cluster is reading accurately. Something all those post have in common that mine does not, the clutch fan seems to be working fine and the car has plenty of coolant I thought the car has smelled kinda warm since i got it but the water temp gauge reads fine right in the middle ( Is there another way to to check if the car is overheating or purposely turning the fan on 24/7 i heard something about a secret menu? ) and I have done a good bit of driving and also sat and let the car idle with no issue before in the 3 days of owning it. I chalked up the warm smell to the grunge that probably grew on the exhaust while it sat, plus the fact that the fan is on as along as the battery is connected even if its been disconnected for a while makes me think its not temp related. Im at a loss could it be the high relay stuck if so where is it located i cant seem to find any details on where the fan relays are, any help is appreciated and if you need me to provide more info on anything just ask!\

Thanks

[edjack]

The FSR only controls the HVAC blower motor.

Unlock the instrument cluster to observe the coolant temp, test 7. http://www.ideaphile.com/bmw/540-obc.html

On your model year, the aux fan is controlled by the engine computer (aka DME). It gets its input from the coolant temp sensor in the radiator outlet hose.

The normal operating temp is circa 105 deg C. The temp gauge is buffered to read a constant temp for most operations.

[JimLev]

Your Aux fan has it’s own PWM circuit built into the motor housing that gets it’s control signal from the DME.
No relays, only 3 wires. Battery + and - and a control wire that goes to the DME.
Very good chance your Aux fan is bad.

[balidawg]

Your Aux fan has it’s own PWM circuit built into the motor housing that gets it’s control signal from the DME.
No relays, only 3 wires. Battery + and - and a control wire that goes to the DME.
Very good chance your Aux fan is bad.

^^^This. Your aux electric fan controller is toast, and you cannot buy it separately. So get a new aux electric fan unit.
That electric fan has always-on voltage supplied, it is NOT switched, so when the fan controller goes bad it can leave the fan running forever.

[ThatSandMan]

thanks every one i talked to a friend of mine who i didn't know was a BMW mechanic and he said what you guys are saying that i need to replace the fan controller so im gonna do that and report back!

[ThatSandMan]

Update for anyone who is reading this in the future, its fixed! Unfortunately you cant just buy the pwm module by itself you have to buy with the whole fan assembly so that's what I did. For $120 off rockauto I got a tyc fan assembly, it took me about an hour to replace and sure enough that was the issue! everything is functioning as it supposed to now and if you don't believe me here's the proof. https://youtu.be/LCp_EMPgfn4

[BimmrMeUpSnotty]

TYC? Hopefully you don’t end up having to do it all over again fr some time.

[balidawg]

The OE Bosch units have been NLA for a few years now.
I think all the electric fans are now made in China, maybe even the genuine BMW one.
It sounds crazy for such a critical component, but I just buy a cheap Chinese fan off ebay for less than $100.

[atobe]

I just buy the behr units, they're also made in china so it's hit and miss. On my 528i the behr replacement died in less than a year so I got a replacement for free. The 540 behr bearing (2012 also made in china) was making noise so I replaced it with another behr. I'm getting pretty good at replacing the aux fan.