The blower final stage fan resistor is known to fail. Symptoms are the heater fan speed varies regardless of the setting, the fan will not turn off when the car is switched off, or the fan will not switch on at all.
Car Problem Reports
BMW M5 Blower Final Stage Fan Resistor May Fail
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JamMasterA, 2003 BMW M5, 83,500 miRookie
no blowing from vent or AC; fixed at dealer
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