Car has engine check light on all the time and is kicking out code 21.. The fan is running as soon as the ignition is turn on. The car runs ok and the temp gauge seems to work, i tried unplugging the orange plug next to the temp sensor and the fan still stays on. The only thing ive done to the car is unplug the ecu and try a different one, noticed the engine check light so put the other ecu back in and the error code is still there ?????????. So could it be the other ecu has blown a sensor if this is possible ? can anyone guide me in the right direction on how to figure this one out..

Thanks

 

Just change the coolant temp sensor.

 

chasey
Imprezas have two coolant temperature sensors, so even if the gauge is showing normal temp the sensor that goes to the ECU might be dead. The picture here shows roughly where it is:
http://www.scoobypedia.co.uk/index.p...wledge/Sensors

(the connector has a brownish coloured top)

 

Code 21 is the engine coolant temperature sensor. So as above change it