I'm trying to sort out a pollution control system faulty problem - did a check and cleanup of the easily accessible sensors under the engine cover. There is what looks like a red sensor to the left of the fuel filter area. I looked at service box and this might be the water in fuel sensor. The top is loose and there is either engine oil or fuel in the body of the sensor. I haven't removed the sensor just in case. Does anybody know what the sensor is? And does it matter that there's some oily liquid in it? The car is a 2.7hdi coupe. The problem is intermittent limp mode - usually when the engine is cool. Running the engine for a few miles then turning it off for a few minutes usually but not always solves the problem. I've changed an EGR and a MAF sensor - neither solved the problem. Many thanks for any info about the red "sensor".