If the fan is not coming on then you may have a faulty auxiliary fan switch. To test the switch, remove the wiring harness that connects to it (on right side, i.e., passenger side on US models, of radiator, a three pin plug). The plug should have three wires coming to it: black/green, black/gray, and brown. Brown is ground, the other two are the control input for the auxiliary fan -- low and high speed, but I don't remember which one is which. With the ignition on, take a jumper from brown to either of the other two. The fan should start. Try both, as each has an independent relay that may have also failed. If your auxiliary fan is not coming on when the A/C is on, you may have a faulty fan, an switch, a blown fuse, or a blown aux. fan low-speed relay.
The test described above actually tests the fan motor (you are switching it on manually). The reasoning is that if it works when controlled directly, then the switch is bad (or a fuse or relay). The bad news is that I think that when you turn on your A/C, the car's electronics override the switch's signal (which is strictly temperature-dependent) and activate the fan in low-speed mode regardless of temperature, unless already runningin high speed mode. This is bad news becasue if your fan is not coming on when your A/C is on, then your fan motor is probably bad. Go ahead and run the test, though. I will be happy for you if I am proven wrong.
If the motor is bad, you will very likely have to buy the entire assembly - fan blades, shroud, and motor - as one replacement part. The replacement switch is not very expensive (about $25-$30). The fan assembly is more costly. I checked bavauto: $530. If the dealer charges $300, as mentioned above, that may be the way to go. Maybe we're not talking about the same thing.
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