Is the fan coming on when it should?
If you're not sure, one way to quick check the fan circuit is to start the engine and turn on the A/C to max. If the fan runs, the fan motor, relay, fuse and wiring are all okay. But this test doesn't show if the temperature switch or temperature sensor and PCM are energizing the fan when coolant temperatures are high.
To check the temperature at which the fan comes on, turn the A/C off and keep the engine running until it reaches normal operating temperature. Most fans should come on when the coolant reaches about 200 to 230 degrees. If the fan does not come on, something in the control circuit is defective. Resistance checks should then be made on the temperature sensor or switch, and a voltage check on both sides of the relay (you will probably need a wiring diagram of the fan cooling circuit on your vehicle to identify the relay terminals and wiring connections).
The fan motor itself can be checked by using jumper wires. Unplug the wiring connector on the fan, and use the jumper wires from the battery to route power directly to the fan. If the fan motor is good, the fan should spin at normal speed when supplied with 12 volts
Thursday, December 10th, 2009 AT 11:21 AM