If the vehicle is an automatic and depending on the year it is located on the lower drivers side of the trans and is called a prndl switch. This for I believe 2005 or older otherwise it is called a transmission range sensor which is located on the valve body inside the trans. This would require removing the trans shift lever, the trans pan and valve body. If this is the case there are two accumulator pistons and springs that will drop down after removing the valve body. Make sure they go back in the same position they came out.