Crankshaft Position Sensor: Description and Operation

CRANKSHAFT POSITION SENSOR - PCM INPUT

Crankshaft Position Sensor:

The Crankshaft Position Sensor mounts to the engine block behind the generator, just above the oil filter.

Timing Reference Notches:

The Crankshaft Position Sensor (CKP) is a Hall-effect sensor. The PCM determines what cylinder to fire from the Crankshaft Position Sensor input and the Camshaft Position Sensor input. The second crankshaft counterweight has two sets of four timing reference notches including a 60 degree signature notch. From the Crankshaft Position Sensor input, the PCM determines engine speed and crankshaft angle (position).

The PCM sends approximately 8 volts to the Hall-effect sensor. This voltage is required to operate the Hall-effect chip and the electronics inside the sensor.

A ground for the sensor is provided through the sensor return circuit. The input to the PCM occurs on a 5 volt output reference circuit.

The notches generate pulses from high to low in the crankshaft position sensor output voltage. When a metal portion of the counterweight aligns with the Crankshaft Position Sensor, the sensor output voltage goes low (less than 0.5 volts). When a notch aligns with the sensor, voltage goes high (5.0 volts). As a group of notches pass under the sensor, the output voltage switches from low (metal) to high (notch) then back to low.

If available, an oscilloscope can display the square wave patterns of each voltage pulses. From the width of the output voltage pulses, the PCM calculates engine speed. The width of the pulses represent the amount of time the output voltage stays high before switching back to low. The period of time the sensor output voltage stays high before switching back to low is referred to as pulse width. The faster the engine is operating, the smaller the pulse width on the oscilloscope.

By counting the pulses and referencing the pulse from the 60 degree signature notch, the PCM calculates crankshaft angle (position). In each group of timing reference notches, the first notch represents 69 degrees Before Top Dead Center (BTDC). The second notch represents 49 degrees BTDC. The third notch represents 29 degrees BTDC. The last notch in each set represents 9 degrees BTDC.

The timing reference notches are machined at 20 ° increments. From the voltage pulse width the PCM tells the difference between the timing reference notches and the 60 degree signature notch. The 60 degree signature notch produces a longer pulse width than the smaller timing reference notches. If the camshaft position sensor input switches from high to low when the 60 degree signature notch passes under the crankshaft position sensor the PCM knows cylinder number one is the next cylinder at TDC.

The PCM uses the Crankshaft Position Sensor to calculate the following:
- Engine RPM
- TDC number 1 and 4
- Ignition coil synchronization
- Injector synchronization
- Camshaft-to-crankshaft misalignment (Timing belt skipped 1 tooth or more diagnostic trouble code).