Camshaft Position Sensor: Description and Operation

Fig 9 Camshaft Position Sensor:

PURPOSE
- Sensor provides PCM with cylinder identification.
- PCM uses sensor input to determine fuel injection sequence and ignition timing.

Fig 10 Camshaft Sprocket:

OPERATION
The sensor generates pulses as groups of notches on the camshaft sprocket pass underneath it (Fig. 10).

The PCM keeps track of crankshaft rotation and identifies each cylinder by the pulses generated by the notches on the camshaft sprocket.
- Four crankshaft pulses follow each group of camshaft pulses.

When the PCM receives 2 cam pulses followed by the long flat spot on the camshaft sprocket, it knows that the crankshaft timing marks for cylinder 1 are next (on driveplate). When the PCM receives one camshaft pulse after the long flat spot on the sprocket, cylinder number 2 crankshaft timing marks are next. After 3 camshaft pulses, the PCM knows cylinder 4 crankshaft timing marks follow. One camshaft pulse after the 3 pulses indicates cylinder 5. The 2 camshaft pulses after cylinder 5 signals cylinder 6 (Fig. 10). The PCM can synchronize on cylinders 1 or 4.

When metal aligns with the sensor, voltage goes low (less than 0.3 volts). When a notch aligns with the sensor, voltage switches high (5.0 volts). As a group of notches pass under the sensor, the voltage switches from low (metal) to high (notch) then back to low. The number of notches determine the amount of pulses. If available, an oscilloscope can display the square wave patterns of each timing event.

Top Dead Center (TDC) does not occur when notches on the camshaft sprocket pass below the cylinder. TDC occurs after the camshaft pulse (or pulses) and after the 4 crankshaft pulses associated with the particular cylinder. The arrows and cylinder call outs on Figure 4 represent which cylinder the flat spot and notches identify, they do not indicate TDC position.

Fig 11 Camshaft Position Sensor:

The camshaft position sensor is mounted in the front of the timing case cover (Fig. 11).

CIRCUIT OPERATION
Circuit K7 supplies 8 volts from the Powertrain Control Module (PCM) to the camshaft position sensor. The K7 circuit originates at cavity 44 of the PCM connector.

Circuit K44 from the sensor provides an input signal to the PCM. The K44 circuit connects to cavity 33 of the PCM.

The PCM provides ground for the camshaft position sensor signal (circuit K44) through circuit K4. Circuit K4 connects to cavity 43 of the PCM.

Helpful Information
Circuit K7 also splices to supply 8 volts to the crankshaft position sensor and vehicle speed sensor.

Circuit K4 also splices to supply ground for the signals from the following:
- Upstream heated oxygen sensor
- Downstream heated oxygen sensor
- Crankshaft position sensor
- Throttle position sensor
- Manifold absolute pressure sensor
- Engine coolant temperature sensor
- Knock sensor
- Intake air temperature sensor
- Vehicle speed sensor

NOTE: The distance between the sensor and camshaft sprocket is critical to system operation. Be sure paper spacer is attached to sensor face when installing sensor. SEE Powertrain Management/Computers and Control Systems/Camshaft Position Sensor/Service and Repair.