Electric Cooling Fan Circuit
Today’s electric engine cooling fans are computer controlled. The control module uses a signal from the ECT or engine coolant temperature sensor to operate the fan motor. Notice in the illustration that the driver grounds the fan relay circuit to operate the fan motor.
Point A is pointing toward the connector to the control module. It’s part of the circuit for the ECT sensor. This sensor changes a voltage signal sent from the control module. Any resistance in this circuit will corrupt the signal affecting fan motor operation.
Point B, like the other points, is pointing at a connector. An open in the circuit caused by a loose plug or pin would result in no fan operation. This is because the circuits driver is unable to ground the circuit controlling the fan motor relay.
A short to ground at point C would cause the relay to close, activating the fan motor whenever the ignition is turned to the on position. This short can also blow the fuse protecting the circuit.
An open at the point D, the connector leading to the fan motor, will result in no fan motor operation. All four of these point to connectors. Connectors and plugs are a common source of problems in electrical circuits and should be visually inspected and tested for continuity and voltage drop if suspected.