Help with an Auxiliary Fan that turns on with key in ignition and doesn't turn off

[AvusBlau//M3]

I have an external fan that turns on with key in the ignition and won't turn off. Its pretty much on constantly and doesn't turn off till the key is removed from the ignition. I don't think its the fan switch. Don't think its the relay either unless its stuck on? Do these fans have a resister and is it possible thats bad? Any help would be great with this! Thanks in advance.

[ross1]

There is no conceivable mode of resistor failure that would cause the fan to run with the key on. A shorted resistor would have it run at high speed when low is called for and an open one would prevent any low speed operation. The fan is controlled by two relays that are both served by an always hot circuit, so a stuck relay would have the fan running with key on or key off. Sounds like the relay(s) are getting a command to run the fan. Removing them one at a time will help you narrow down which speed is being called for. Your troubles most likely rest with the controls which are what provide the marching orders to those two relays. Post more specific info about your car as there are several versions of the climate controls over the years.

[AvusBlau//M3]

there is no conceivable mode of resistor failure that would cause the fan to run with the key on. A shorted resistor would have it run at high speed when low is called for and an open one would prevent any low speed operation. The fan is controlled by two relays that are both served by an always hot circuit, so a stuck relay would have the fan running with key on or key off. Sounds like the relay(s) are getting a command to run the fan. Removing them one at a time will help you narrow down which speed is being called for. Your troubles most likely rest with the controls which are what provide the marching orders to those two relays. Post more specific info about your car as there are several versions of the climate controls over the years.

1991 m5

[M60B40Bimmer]

There is no conceivable mode of resistor failure that would cause the fan to run with the key on. A shorted resistor would have it run at high speed when low is called for and an open one would prevent any low speed operation. The fan is controlled by two relays that are both served by an always hot circuit, so a stuck relay would have the fan running with key on or key off. Sounds like the relay(s) are getting a command to run the fan. Removing them one at a time will help you narrow down which speed is being called for. Your troubles most likely rest with the controls which are what provide the marching orders to those two relays. Post more specific info about your car as there are several versions of the climate controls over the years.

I have the same issue on one of my 1990 535i/5's. Fan turns on med-high (pretty loud) with ignition on.

[zubbie]

Which fan are your referring to? HVAC, rad or perhaps the DME fan? If it's the DME (ebox) fan then it turns on with ignition and runs on high if temps rise in the ebox. Perhaps your temp sensor is fubared and the fan wants to run on high all the time.

More info http://www.bimmerforums.com/forum/sh...an-Replacement or do a search for ebox fan.

[AvusBlau//M3]

Which fan are your referring to? HVAC, rad or perhaps the DME fan? If it's the DME (ebox) fan then it turns on with ignition and runs on high if temps rise in the ebox. Perhaps your temp sensor is fubared and the fan wants to run on high all the time.

More info http://www.bimmerforums.com/forum/sh...an-Replacement or do a search for ebox fan.

Its the fan in the front of the radiator.

- - - Updated - - -

So after some digging last night and checking the fan switch it appears that the previous owner ridged the wiring to kick on with key in ignition. Not sure why he had it that way but Im going to solder the wires back later today and see what happens. Now its making me question what other things were ridged on this car!

[mgoods50]

Lol beat me to it. I've seen this a dozen times. One of the first things I used to check in that situation

[zubbie]

Probably an attempt to deal with an overheating situation. Not a good sign.

[ross1]

Its the fan in the front of the radiator.

- - - Updated - - -

So after some digging last night and checking the fan switch it appears that the previous owner ridged the wiring to kick on with key in ignition. Not sure why he had it that way but Im going to solder the wires back later today and see what happens. Now its making me question what other things were ridged on this car!

Yep, Not a good sign.
How is this rigged?
I was about to suggest unplugging the temp sensor on the radiator which would likely have stopped the fan but seeing you were in California I figured driving with no fan was a bad idea. The easiest way to rig the fans to run with key on would be to ground either the low or high speed wire at the temp sensor. If someone did this rigging at the switch they really didn't understand the car's circuits.
The whole work around could simply be the result of a failed temp sensor and someone that shouldn't be fixing cars.
Good luck

[AvusBlau//M3]

Probably an attempt to deal with an overheating situation. Not a good sign.

Yep, Not a good sign.
How is this rigged?
I was about to suggest unplugging the temp sensor on the radiator which would likely have stopped the fan but seeing you were in California I figured driving with no fan was a bad idea. The easiest way to rig the fans to run with key on would be to ground either the low or high speed wire at the temp sensor. If someone did this rigging at the switch they really didn't understand the car's circuits.
The whole work around could simply be the result of a failed temp sensor and someone that shouldn't be fixing cars.
Good luck

Lol beat me to it. I've seen this a dozen times. One of the first things I used to check in that situation

The funny thing about this situation is that the guy was supposed to be a master mechanic at the shop he worked at. I questioned it when I was asking him a few things on what was done, etc and he couldnt really tell me much. Possible the mechanical fan is on its way out and wasnt cooling efficiently so he rigged it to stay on constantly. Dont think theres any major issues going on with the car as I was able to get it home and it was a pretty long drive home. Ill just go through the car more thoroughly. Thanks for all the posts and help!

[uxtcmenuts]

I have had similar problems with our aux fan but now it has decided to just stay on all the time and won't shut off even with the car off and does not shut off even with the car off and drains the battery could the be a relay problem. replaced the fan switch on the radiator less than a year ago. any Ideas?

[moroza]

I have had similar problems with our aux fan but now it has decided to just stay on all the time and won't shut off even with the car off and does not shut off even with the car off and drains the battery could the be a relay problem. replaced the fan switch on the radiator less than a year ago. any Ideas?

Punctuation, please.

You could either have monkeyed wiring like the OP, or the relays could be stuck on. Pull the relays (look up where they are on your car; I don't know offhand) to see if the fan shuts off. If it doesn't, the wiring has been modified intentionally or unintentionally (melted or bare wiring somewhere). If it does, find a multimeter and check out what's hot and what's not (and under what conditions, like key in or out) in the relay sockets.

[Racerhoze]

I had a bad relay on my 535 that would get stuck. I got in the habit of punching the drivers side fender after shutdown to kick the fan relay off. Replaced the relay with a minty fresh one and my problem was solved.

[zkd]

if there is too much current going through the relay, and the relay is old then the fan will stay on.. replace the Aux Fan relay.

[ross1]

. I got in the habit of punching the drivers side fender after shutdown to kick the fan relay off.