Radiator fan

Well, if I understand your chart correctly, when the car is warmed up, the resistance should be close to zero.

Well when we unpluged the sensor, the fan kicked on.
Electricly speaking, when I unpluged that sensor, the ohms reading across the PLUG unit itself should have been maximum, or infinate as there would be nothing connected to the 2 plugs in the wire harness.

And according to your chart, the higher the reistance, the colder the engine.

This makes me think the problem is not the sensor, but maybe the controller box.

Does that make sense? Thanks for your reply.

IS there another temp switch on the thing? I finally got around to testing it, and according to the chart above, it checked out ok.

Guess im going to have to take it in for a scan.

Thats the one I am checking, its right next to the thermostat.

I couldn't quite make out what item you ment by the drawing, I even got a copy of it to enlarge, and still could not make it out.

THIS is what I have checked out based on the information posted here so far.

Im not an automotive mechanical genius as a tool and die machinist, however, I have been doing electronics since I got my first ham radio licence at age 14.

According to the first response above, the coolant tempature sensor is basicaly a variable resistor.

The plug unit, that is the wire harness that attaches to the sensor, is compeating a circut, that is being monitored somewhere.

According to the chart, as the tempature of the engine goes up, the resistance measured should go down.

I.E. If I unplugged the unit and put a jumper wire into the plug, there would be ZERO ohms or ZERO resistance. Resulting in a "closed circut" or a "short". Meaning there is supposed to be a load of some kind there, but there is nothing, thus a short has occured.

Again, according to the chart, when the engine is cold, the resistance should be high. Taking that jumpe wire out, should give me infinate or maximum resistace. Since nothing is plugged into the sensor wire plug, there is no current or voltage flow, thus this results in an OPEN circut.

The Fan is supposed to kick on ONLY when resistance is low or non existant, and current or voltage in the crcut is still able to flow thru the circut.

Again, when I unplug the wire harness from the temp sensor, (an open circut) the fan turns on regardless of the tempature of the engine.