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.
Wednesday, October 31st, 2007 AT 3:46 AM