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aux. fan not working

137K views 45 replies 17 participants last post by  GlynDanks 
#1 ·
my aux fan is not working nor turning on when the a/c is on. I replaced the fan switch that goes in the lower hose attached to the rad when I did the cooling system overhaul.
what else could it be the cause?


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#8 ·
my aux fan is not working more than a year
 
#16 · (Edited)
Don't get excited too soon! That DIY by "PENER" on bimmerforums is for 1997-98 models.

Your 1999 model has a different setup. Search for info. Very often the whole assembly has to be replaced. But again check to be sure that the Aux Fan is the culprit.
The 1999 Aux Fan is pricy though, about $320-350 range or so. Check realoem.com for PN.
 
#20 ·
Here is my two bits worth. The aux fan on my 99 528 came on nearly all of the time when I first bought my car and I just thought this might be normal. As it ultimately turned out the reason it was coming on all of the time was that it was defaulting to the radiator temp sensor. But, when I overhauled my cooling system I found that the sensor on the bottom radiator hose was unplugged. So, I plugged it in and then the fan would not come on at all. I replaced the sensor with a new one and still no fan; no matter how warm the engine got or how high the pressure in the AC. After driving myself nuts in every way trying to figure it out, I finally took it to a high quality indy shop. They hooked it up to their super scanner and got a message that an aux fan code was missing in the control module. They disconnected the battery for ten minutes, reset the codes and now the fan works just fine.
 
#27 ·
For the cross-linked record, today, JimLev provided nice aux fan test info:
- E39 (1997 - 2003) > Aux Fan Help

The fan is controlled by the dual temp switch on the side of the radiator and the HVAC system.
Stage 1 is low speed from the HVAC panel or the 91 deg switch on the radiator and relay K21.
Stage 2 is controlled by the AC high pressure switch and relay K22.
Stage 3 (high) is controlled by the 104 C deg switch on the side of the radiator and relay K201, which gets power from fuse F75 (50 amp) behind the glove box. F20 and F105 powers K201.

You said the fan comes on when you turn the AC on so Stage 1 (low) is working which means the 2 resistors are good.
Pull the connector off the dual temp switch and jump it to see if you can get.
Jumping pins 1 to 2 should make it run at high speed and pins 1 to 3 for low speed.
 
#28 ·
#30 · (Edited)
Mine did that just before it died, mine would turn on, but would stay on the highest fan speed setting. Sounds ridiculously loud right? The cheapest OEM fan i've found is from ecstuning, or just get a used one for cheap.
 
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