SERVICE ENGINE SOON LIGHT/ POOR GAS MILAGE

Knock sensor is located on the block usually under the intake. nissan has problems with these sensors. i have chaunged plenty of these on nissans in the past year. this has no affect on your gas mileage. this sensor picks up misfires on the engine. sometimes you might have rough idle and can't feel it in the drivers seat but the knock sensor can. i would suggest maybe a tune up spark plugs, air filter, fuel filter first before going to take apart a bunch of things to change a sensor. the sensor is designed to pick up any differences in motor quality and will throw the engine light on. sometimes the problem is the knock sensor, or there is an underlying cause that the knock sensor is reading.