Common problems with crankshaft position sensors include connector pins that are loose, cracks in the sensors and improper gaps between the reluctor wheel and the sensor tip. Faulty sensors can prevent a car from starting and cause engine stalling. Failed crankshaft position sensors can activate the check engine light.
When crankshaft position sensors are failing, they cause sporadic stalling or long cranking in damp weather, or in hot engines. Hot cars that stall but start again once their engines cool may have deteriorating crankshaft position sensors. Using an oscilloscope to check the sensors' signals is a precise way of testing the equipment. Hall-type sensors require testing the ground signal and the reference voltage, while pick-up coil type sensors require checking the sensors' resistance. Technicians replace the sensors when the resistance is greater than or less than a vehicle's manual specifies.