Camshaft Position (CMP) Sensor - (From 99MY)
The CMP sensor is located at the front of the engine block, above and behind the crankshaft pulley. The sensor is clamped into position by means of a single bolt. An 'O' ring is used to seal the interface between the sensor and the aperture in the engine front cover.
The sensor has three wires which terminate in a multiplug secured to a bracket on the left of the crankshaft pulley. A short link lead is used to connect the sensor to the engine harness. The wires to the sensor have the following functions:
- Power supply from engine compartment fusebox
- Camshaft input signal to ECM
- Screen to chassis ground connection
The CMP sensor is a Hall effect sensor which produces four pulses for every two engine revolutions. The sensing element is positioned less than 2mm from the side of the camshaft gear wheel. The camshaft gear wheel has four slots machined at 90°intervals which allows the identification of four cylinder positions every camshaft revolution. Cylinder recognition is used to enable sequential fuel injection and knock control and is also used for diagnostic purposes. The slots in the camshaft gear wheel are shaped to provide unequal timing pulses for determining TOC on No.1 cylinder. The camshaft and crankshaft drives must also be correctly aligned, since the ECM uses the crankshaft "missing teeth" marker to determine crankshaft and camshaft position and provide a reference mark which is 60° BTDC on No.1 cylinder.
The CMP sensor uses the Hall effect to act as a magnetic switch for switching battery voltage on or off depending on the position of the camshaft gear wheel in relationship to the sensor. This results in a square wave input between 0 and 12V at the ECM input pin.
Symptoms of a CMP sensor failure include the following:
- Ignition timing reverts to default values from ECM memory with loss of cylinder correction.
- Loss of active knock control and diagnostics.
- Loss of cylinder identification for misfire diagnostics.
- Loss of quick synchronization of crankshaft and camshaft for cranking/start up.
- Fuel injection could be 360°out of phase at engine restart.
- Front HO2S sensor ageing period diagnostic could become disabled.
The cause of CMP sensor failure may be attributable to one of the following conditions:
- Sensor open circuit.
- Sensor signal line short circuit to vehicle battery supply.
- Sensor signal line or voltage supply line short circuit to vehicle ground.
- Incorrect fitting of the sensor.
- Excessive camshaft gear wheel tolerance.
- Excessive camshaft endfloat.
- Camshaft and crankshaft misalignment.
- Speed signal correlation with CKP sensor signal.
Should a malfunction of the component occur the following fault codes may be evident and can be retrieved by Testbook:
- P0340 - (Signal open & short circuit to vehicle supply or ground).
NOTE: It is physically possible to interchange the camshaft gear wheel fitted to pre-99MY and post-99MY vehicles. However, because the GEMS and Motronic systems are incompatible, an incorrect camshaft signal will be received by the ECM and a P0340 fault code will result.