The 1993 Buick Century's cooling fan is computer-operated. The circuit consists of the fuse, relay, coolant temperature sensor, computer and the fan. The power is supplied through a fuse to the relay which, when activated, supplies power to the fan. The computer receives a signal from the coolant temperature sensor in the form of increased resistance to ground as the engine temperature rises. As a result of this signal, the computer activates the relay and turns the fan on. The computer also recognizes a signal when the air conditioning is turned on and activates the fan on a continuous basis.
Check the cooling fan fuse in the fuse box on the driver's side fenderwell and replace it if necessary. If it is defective, the metal strip in the middle of the fuse will be broken. Locate the coolant temperature sensor near the thermostat housing. The sensor will have two wires on its connector.
Start the engine and unplug the sensor. If the fan comes on, the sensor is bad because you just created infinite resistance. If the fan does not come on, reconnect the sensor.
Check the relay located behind the driver's side headlight. This is the fourth relay to the right as viewed from the driver's seat. It has four wires: two heavy gauge -- one red and one black with a red stripe -- and two thinner gauge -- one brown and one green with a white stripe.
Pull the electrical plug out of the relay. Connect the black lead of a voltmeter to a good ground and use the red lead to probe the red wire in the harness. There should be battery voltage of 12 volts. If there is no voltage, the red wire from the fuse to the relay is bad. If there is voltage, plug the connector back in.
Unplug the cooling fan connector. Check the black wire with a red stripe for power, using the red lead from the voltmeter. If there is no power present, the relay is bad. If there is voltage, the fan is bad.
