Camshaft Position (CMP) Sensor There are two CMP sensors which are located on the upper timing case covers. The CMP sensors monitor the position of the camshafts to establish ignition timing order, fuel injection triggering and for accurate Variable Camshaft Control (VCC) camshaft advance-retard timing feedback. The CMP sensor is a Hall-effect sensor which switches a battery fed supply on and off. The supply is switched when the teeth machined onto the camshaft gear pass by the tip of the sensor. The four teeth are of differing shapes, so the ECM can determine the exact position of the camshaft at any time.
ENGINE MANAGEMENT SYSTEM – V8 DESCRIPTION AND OPERATION 18-2-21 CMP Sensor Unlike an inductive type sensor, a Hall-effect sensor does not produce a sinusoidal output voltage (sine wave. Instead it produces a square wave output. The wave edges are very sharp, giving the ECM a defined edge on which to base its calculations. An implausible signal from the CMP sensor will result in the following: l The MIL lamp illuminated after de-bouncing the fault (NAS only and EU) l Loss of performance, due to the corrective ignition strategy being disabled. A default ignition map is used which retards the timing to a safe position l Injector operation possibly 360 ° out of phase, i.e. fuel injected during exhaust stroke rather than during compression stroke l Quick crank/cam synchronisation on start-up feature disabled l Some Oxygen sensor diagnostics disabled. In addition, the ECM will store a relevant fault code and capture the input signal supplied by the engine coolant temperature sensor, the engine load calculation and the engine speed at the time of failure. TestBook/T4 will display the live readings from the CMP sensor.