I need to follow-up on my last post regarding the testing of the aux fan. There are many posts on aux fans, but not many on X5 aux fans! Safe to assume they are not all the same!


Do not jumper fan control signal as mentioned in my previous post. This is not a valid/proper test for the X5 aux fan and it will not verify proper operation. The aux fan requires the presence of a proper pulse width modulated (PWM) signal in the 5 volt peer-to-peek range. The application of 12 volts on the control signal could damage your fan. Do not do this.



The best test for your fan is to let the X5 reach normal operating temperature, turn on the AC to full blast lowest temperature. The fan should come on period.


If the fan does not come on with this test, unplug the fan connector and carefully measure the DC voltages at the connector. If you have +12 Battery Voltage on the large wire and about 3.8 DC volts on the small control wire. Then the control circuit is good and your fan is not responding*** Be very careful measuring the control signal not to short it out. The control signal is coming from the control computer!


Optional: While making the control signal measurement, have a helper turn on and off the AC, the voltage on the control signal should change as it switches on and off. If you were to look at the control signal with an oscilloscope you would see the duty cycle change between 5% to 50%. The most important point is that the average DC voltage is changing. Do not make any assumptions regarding the level of the voltage with it on and with it off. If control voltage changes, the duty cycle is changing so it safe to assume the signal is good.


*** I took the old broken fan apart to satisfy my curiosity. I found a very complex control circuit board with many many electronic components. It appeared that 4 of the driver transistors were fried.


Having completed this DIY job and seeing the inside components of this fan, I highly recommend only using an OEM replacement fan. (Siemans) This fan is internally well built/engineered and is a very complex component of your car. This Job involved a good bit of labor/time to remove and replace. Do it once, with good parts!