What does the crankshaft position sensor do? The crankshaft position sensor along with the camshaft position senso? is used to control ignition timing and lets the computer know when to inject fuel and provide spark sequence How do you know you need your crankshaft position sensor replaced? The vehicle does not start The check engine light is on The vehicle misfires How is the crankshaft position sensor replaced by a mobile mechanic? The vehicle is scanned for trouble codes The crankshaft position sensor is removed and replaced All trouble codes are cleared The vehicle is checked for proper operation of the car How important is having your crankshaft position sensor replaced? Without a properly working crankshaft position sensor the vehicles computer system will not receive important information and the vehicle will either not start or misfire while you are driving it.