Crankshaft Position (CKP) Sensor
Crankshaft Position (CKP) Sensor
the CKP sensor is located in the engine block, just below number 4 cylinder. It protrudes through the cylinder block and is positioned adjacent to the face of the flexplate. the sensor reacts to a toothed reluctor ring incorporated into the flexplate to ascertain engine speed and position information. the sensor is located on a split spacer and is secured in position by two tube spacers and nuts. the split spacer is 18 mm thick on vehicles fitted with automatic transmission. the thickness of the split spacer determines how far the sensor protrudes through the cylinder block and therefore sets the position of the sensor in relation to the reluctor ring. the sensor and the spacer are covered by a protective heat shield. the sensor has three wires attached to it; two signal wires and a screen. the sensor earth screen is connected to chassis earth through the ECM.
the crankshaft sensor is an inductive type sensor which produces a sinusoidal output voltage signal. This voltage is induced by the proximity of the moving reluctor ring which excites the magnetic flux around the tip of the sensor when each tooth passes. This output voltage will increase in magnitude and frequency as the engine speed rises and the speed at which the teeth on the reluctor ring pass the sensor increases. the signal voltage will peak at approximately 6.5 volts if connected to the ECM (further increases in engine speed will not result in greater magnitude). the ECM neither specifically monitors nor reacts to the output voltage (unless it is very small or very large), instead it measures the time intervals between each pulse (i.e. signal frequency). the signal is determined by the number of teeth passing the sensor, and the speed at which they pass. the reluctor ring has 58 teeth spaced at 6° intervals, with two teeth missing to give the ECM a synchronization point.
the signal produced by the crankshaft position sensor is critical to engine running. There is no back-up strategy for this sensor and failure of the signal will result in the engine stalling and/or failing to start. If the sensor fails when the engine is running, then the engine will stall, a fault code will be stored and details captured of the battery voltage, engine coolant temperature and intake air temperature at the time of the failure. If the signal fails when the engine is cranking then the engine will not start and no fault will be stored, as the ECM will not detect that an attempt had been made to start the engine. In both cases the tachometer will also cease to function immediately and the MIL lamp will be permanently illuminated.
During the power-down procedure, which occurs when the ignition is switched off, the ECM stores details of the position of the crankshaft and camshaft sensors. This enables the ECM to operate the injectors in the correct sequence immediately the engine cranks, to produce a quick engine start which serves to reduce emissions when the engine is cold.