There's two temperature sensors on the side of the thermostat housing. The one with the single wire is for the gauge on the instrument cluster. The one with two wires is for the engine computer. The computer will turn on the radiator fan relay and the "Check Engine" light when you unplug this sensor. The computer doesn't know actual engine temperature with the sensor unplugged so it runs the fan as a precaution in case the engine is overheating. The Check Engine light is turned on per government mandate because any sensor problem can result in excessive emissions.
To test the system, just unplug that two-wire sensor. If you hear the fan relay click about one or two seconds later, but the fan doesn't run, check for proper operation of the backup lights. If they work, suspect a bad fan motor. Unplug the fan and run a pair of wires directly from the battery to test its operation. If the backup lights and the fan do not work, suspect a burned-open fuse link in the harness next to the left strut tower. Possible causes are a shorted fan motor or a wiring harness under the battery tray has rubbed through so bare wires are touching bare metal.
Saturday, April 11th, 2009 AT 2:47 AM