BMW Questions? Ask a BMW Repair Expert for Answers.
I am assuming the vehicle is overheating, the fan will only come on when the vehicle reaches a certain temperature, if that temperature is not reached the fan will not come on. Here are a few things to consider in finding the problem. Isolating the problem may require special equipment to check and see what the computer is seeing verses what the computer is actually doing.
The electrically operated engine cooling fan is controlled by the engine control module and will operate at variable speed depending on coolant temperature and vehicle speed.As engine coolant temperature increases, condenser fan speed will increase accordingly. A pulse width modulated signal is sent from the engine control module to the cooling fan. An integrated output stage unit on the cooling fan will determine the requested speed from the engine control module and activate the fan.Verify that radiator outlet temperature sensor in hose is connected and will provide a resistance which changes with temperature. The thermostat should open when engine is run hard and outlet temperature should change accordingly. If outlet hose doesn't get hot enough, the thermostat isn't opening properly.Small Black/Green wire going to fan should be a square wave signal which originates at the engine control module. If no signal is present when fan should be running, inspect for wire damage between engine control module and cooling fan. A heavy gauge Red/Blue wire should have battery voltage and the Brown wire is a ground.Verify proper coolant flow by looking into coolant reservoir and verify that a stream of coolant shoots across the opening when engine is running at about 1500 rpm. The stream should be quite strong. If not, the water pump is not pumping well.
Which wire has no power?