Crankshaft Speed and Position (CKP) Sensor - (From 99MY)
The CKP sensor is located at the lower, rear LH side of the engine below cylinder number 7. The CKP sensor is protected by a heat shield which is attached to the rear flange of the engine block by two M5 bolts. The CKP sensor itself is located on two studs and fixed in position by two M5 nuts and 18mm spacers. The sensor has a flying lead which terminates in a 3-pin multiplug that connects to the engine harness and is mounted to a bracket to the rear of the left hand cylinder head.
The tip of the CKP sensor protrudes through an aperture in the engine block rear flange, adjacent to the outer circumference of the flywheel. A 60-tooth reluctor ring is included on the flywheel which provides the reference signal to the crankshaft position sensor.
The ECM uses the signal produced at the CKP sensor to determine the position of the crankshaft to enable accurate ignition and fuel injection timing. The ECM also determines the engine speed at any particular instance through analysis of the frequency of fluctuations induced in the CKP sensor as the teeth of the reluctor ring pass by the sensor tip.
The CKP sensor is a variable reluctance sensor, and contains a permanent magnet and soft iron core surrounded by a copper winding. As the reluctor ring passes by the sensor tip it causes a voltage to be induced in the sensor, consequently the CKP sensor does not need a power supply for operation. The signal wires of the CKP sensor are surrounded by a grounded screen to prevent noise being induced in the signal wires and causing a spurious interference signal being passed to the ECM
NOTE: When fitting a CKP sensor, ensure no ferrous metal has been attracted to it by its magnet. Ensure the sensor pin is straight and undamaged.
The reluctor ring teeth are spaced at 6° intervals and are 3° wide. Two of the reluctor ring teeth are removed, to provide a reference mark which indicates when the crankshaft is at 60° BTDC for number 1 cylinder. The remaining 58 teeth cause an AC voltage to be induced in the sensor pick-up, with the amplitude of the signal increasing with rising engine speed. The voltage generated is an analogue signal capable of peak amplitude voltages of up to 300V.
The distance of the tip from the top of the reluctor ring teeth is important as the amplitude of the detected signal will be reduced in proportion to an increase in the gap between the sensor tip and the top of the reluctor ring teeth. If the air gap becomes too wide, the CKP signal could become too weak and possible misfires could occur. Spacers are included in the CKP sensor kit which are used to ensure the correct gap between the sensor tip and reluctor ring teeth.
The ECM uses the falling edge of the signal waveform as its reference for each reluctor ring tooth. Consequently, if the input signal wire and reference ground wire are inadvertently reversed, the ECM will react by providing a 3° advance in ignition timing.
If the crankshaft sensor fails, the engine will stop and fail to restart. There is no back-up strategy or limp home facility programmed into the ECM. If a fault occurs whilst the engine is running, the engine will stall and a fault code will be stored in ECM memory. If the fault develops while the engine is not running, the engine may not be capable of starting and no fault code will be available. In this case, the MIL light will still be illuminated.
In the event of a CKP sensor signal failure, the following symptoms may be observed:
- Engine cranks but fails to start
- MIL remains on at all times
- Engine misfires (CKP incorrectly fitted)
- Engine runs roughly or stalls (CKP incorrectly fitted)
- Tachometer fails to work
Possible causes of CKP sensor failure include the following:
- CKP sensor not fitted correctly (or assembly loose)
- Incorrect length spacers fitted
- Sensor/wiring open or short circuit
- Sensor bent or damaged by reluctor ring
- Water ingress
- ECM unable to detect the software reference point.
Whenever a new CKP sensor is fitted or the flywheel is removed, the adaptive values have to be reset using Testbook.
Should a malfunction of the component occur, the following fault codes may be evident and can be retrieved by Testbook:
- P0335 - (reference mark is outside search window with engine speed above 500 rev/mm for 4 revolutions.
- P0336 - (incorrect number of teeth detected ± 1 tooth between reference marks.
In addition to crankshaft position, the ECM also uses the CKP sensor signal to determine engine speed. The ECM shares the engine speed information with the electronic automatic transmission (EAT) ECU by transmitting the data via the CAN link. Engine speed output is also provided to the instrument pack (tachometer), for which the output signal is scaled down to 4 pulses per crankshaft revolution.
The ECM also has a quick start facility, where the position of the crankshaft and camshaft are memorized when the engine is stopped. This stored information is used to facilitate immediate sequential fuelling during cranking.