Basic Fan Circuits

Simple fan circuit explained.

The fan in the diagram above is controlled by a driver in the control module. When a preset engine coolant temperature is met the PCM grounds the circuit activating the fan motor. If the circuit is grounded before the control module the circuit will be activated any time the ignition is switched ON.

The other choices are open circuits. An open at point B is most likely caused by a burned fuse. A fuse is a protection device, its fusible element will burn resulting in an open circuit when too much amperage is drawn, like the short to ground in the circuit. An open at point C stops the power flow to the motor. Without power the motor will not function. An open at point D would remove the circuit’s necessary ground also resulting in no fan motor operation.