I couldn't find any thread detailing what may be happening here, so here goes nothing. 2 months ago my aux fan went bad, so I ordered a Dorman and replaced it, it worked for 3 weeks then died. Since I have a lifetime warranty on the part, I got another and put it in. Fast forward to 2 days ago, the aux fan wasn't kicking on again and thought it was weird that I would get 2 defective units in a row, so I started playing with wires. It's the 2 connector unit with the large block below and the 2 thin wires up top. In any case, when both 4 and 2 wire are plugged in, it doesn't work. When the 2 wire is unplugged then it works while the car is on and when I stop the car it kicks off which is ok by me. My question is, why would this behavior exist and what is the culprit? Could it be a relay or possibly the coolant temp sensor at the root of the issue? Have any of you ever ran into this?

 

First off....
What is the year and production month....wiring changes DID happen over the years...
Secondly....it appears you are talking about the radiator fan?
Sometimes the aux fan is refered to as the PS fan....but does not sound as such from your post....

 

May of 2002 Cooper S. And, yes I am talking about the radiator fan.

 

Take a picture of the 2 wire connector...
Pretty sure that if it is the ovalish shaped one, that one is the power plug for the PS cooling fan....
MOST cars were wired this way till production 1-2005 cars....many cars were rewired....
Issue is the ps fan gets stuck (seals go bad, water, sand or even a plastic bag or ice chunks) and it can blow the fuse that powers it....thus de-powering the relay that runs the rad fan....
Not sure what interaction is with your wiring....yours has the relays in a different spot than newer cars...thus the change in which fan to order based on the plugs....

 

Sorry, been a while had some stuff come up. In any case, here's a pic of my 2 wire connector, it's the oval one. Is this supposed to be a different connector these days? Or was this part of a recall that didn't happen on my Mini?

 

Are you sure the fan isn't still working? The low speed comes on at like 220. High at 235.

 

It turns out the fan works when I turn on the AC, meaning hitting the AC button. If I don't have it on, then the fan doesn't ever come on because the top plug is unplugged. What does the top plug even go to? Does it go to the coolant temp switch?

 

pretty sure (from the shape of the plug) that is the plug that powers the PS cooling fan...


http://www.waymotorworks.com/oem-pow...ering-fan.html
If the wiring change was done...this plug is either CUT off...of just left hanging....
the change was part of a campaign, not recall...basically if you had an issue while under warranty, or just had a good dealer, they wold change the wiring to match the 2005+ PRODUCTION cars...
Not sure what you having going on...but the fan runs VERY little unless the car has been run pretty hard or it is a hot day....or the ac is on...
remember, the cast iron block is a BIG heatsink....

 

The radiator fan has a single wire with 2 connectors that come off it, 1 that's the now unplugged 2 wire connector, the other is the 4 plug/3 wire connector. The ps fan works independent of the other 2 being plugged in/unplugged.

 

Went ahead and got a replacement radiator fan since it has a lifetime warranty through O'Reilly. When I got it out, the resistor had a couple of what looked like burnt spots on it, so apparently the unit malfunctioned just on the low side but was fine on the high side with the 2 prong connector unplugged. Whatever, it's fixed now and I'm back on my way with it cycling like it's supposed to instead of being constantly on when the key is turned to the on position.

The new one I got I ended up having to cut the wire since it came with a different 2 prong connector and strip it to the desired length again. Instead of crimping it this time, I heat shrinked the individual wires and got a much better result aesthetically.

 

2 weeks later, my radiator fan is still having the same issues and I've replaced the fuses, relays, and radiator fan. The only thing left at this point is the coolant temperature sensor. Has anybody replaced one of these yet and where is it located? It's only a $25 part, but it's the only thing left until I start tracing electrical gremlins.

 

I have a 2003 R53 that I pulled out all the A/C. After that, the fan would run full speed as soon as I turned it on and stay at full speed. I realized there was a sensor on the A/C line that was unplugged. When I took the sensor and plugged it back into the car(the sensor is now just open to the air) the fan runs now at a slower speed. I know this is not the same problem as you are having , just wanted you to now about another sensor that affects fan speed.

 

Yep, a/c pressure sensor kicks the low fan on at 8 bar and high speed at 18 bar or above
in addition to the coolant sensor kicking it on at 221F (105C) and 234F (112C) respectively.