Technical Radiator Cooling Fan Running Constantly

[crawfie]

recently bought a 2005 Scudo 2.0JTD with a single radiator fan which has developed a radiator fan problem. when i turn on the ignition the overheat light is on and when i start the engine the fan comes on at high speed and stays on, other symptom is the temperature gauge doesn't work and overheat light is on along with the flashing stop light, fan continues to run when i turn off the ignition. any help appreciated, I've had the van scanned and it shows P0115

 

[RalphM]

Check the connections on the temperature sensor this is likely on the thermostat housing
just taking the plug off and cleaning it may work.

 

[crawfie]

replaced temperature sensor with the same result fan still runs and fault code P0115 still showing also opened up the loom to the sensor checking for breaks/shorts none found. is there the one sensor ? I swapped out the green one on the thermostat housing

 

[RalphM]

If there's another it's likely on the radiator it.s self.

 

[ZaphodB]

A quick search reveals this is an NTC (negative temperature coefficient) sensor ... just a resistance which varies with temperature.

If you check with a multimeter on the two terminals of the sensor you should get a resistance reading, which will reduce even further if you stick the sensor in a cup of hot water.... and come back up to the original if the end is dunked into cold water.

So if the ECU/vehicle thinks it's too hot ... the resistance will be low ... if the sensor is ok (after testing above) it could be a shorted cable