remove engine cover and locate injectors - should be on front of engine each with a hex nut and pipe attached, at least one (I think only one) of the injectors will have an electrical connection to it - trace the connection back to plug. Lift oout of bracket unplug and clean contacts. I don't have one of these engines so can't be more specific. I amm assuming that the ecu uses the sensor to workout how far through the fuel injection cycle the engine is. ( I think this engine has dual spring needles, low pressure initial injection against first spring followed by complete injection against the second spring - don't know which the needle sensor senses) Of course there may be a needle control valve elsewhere in the system - someone else will be along in a minute to correct me I'm sure.