CKP is the sensor, without operation of the fuel injection system is impossible. Defects in CKP inevitably lead to engine failure and the car will not run. Crankshaft position sensor (CKP) is an electromagnetic sensor by the help of which the fuel injection system makes synchronization of the fuel injectors operation and the ignition system. СКР sensor sends signal for the speed and the position of the crankshaft to the onboard controller. This signal is a series of repetitive electrical voltage impulses, generated by the sensor when the crankshaft is rotating. Based on these impulses, the onboard controller controls the fuel injectors and the ignition system.
A typical СКР sensor is shown in fig.1.
Working principle of the crankshaft cogwheel – CKP sensor pair
CKP is placed on the console to the cogwheel of the crankshaft.
Fig. 2 Fig. 3
An air gap is placed between the sensor and the cogwheel. This gap should be about 1mm ± 0.4mm and is achieved by selecting the appropriate washers (fig. 2 and fig. 3).
The crankshaft cogwheel is manufactured as a special disk which has usually 58 teeth in each 6 degrees. There are two missing teeth which are used to generate synchronization pulse (fig. 2 and fig. 3). Crankshaft rotation causes change of the sensor magnetic field and thus creating voltage pulses. Through the pulse synchronization from the CKP sensor, the onboard controller determines the position and speed of the crankshaft and calculates the exact moment of operating the fuel injectors and the exact moment for generating the spark. The beginning of the 20th tooth (after the missing ones) of the cogwheel matches with the top dead center (TDC) of the first and the fourth cylinder.
Cogwheel can be cast, non-metallic or damper (with rubber insulation). During the exploitation of the car, wear of non-metallic cogwheel was not observed. The only thing that should be monitored is to prevent penetration of small particles and dirt between the teeth. If the cogwheel is with damper, its state should be monitored for a damper damage because it can lead to engine problems. When performing repairs you should be careful not to allow deformation of the cogwheel because this can lead to an engine collapse. Visual observation of the cogwheel can be done from the right front wheel side, as shown in fig. 4.
Used types of sensors
СКР are divided into two types:
- Hall sensor effect
In the inductive ones, the sensitive element has a magnetization core and a copper conductor winding mounted on an isolated coil.
Hall sensors use the “hall effect” expressing the impact of magnetic field on semiconductor sensor.
Typical symptoms of defective CKP and crankshaft cogwheel
In case of failure of CKP or crankshaft cogwheel, the onboard controller records a fault event and illuminates the "CHECK ENGINE" indicator lamp. Following symptoms can be assigned to faults of these elements:
- erratic idling
- spontaneous increase and decrease of the engine speed;
- engine stop;
- engine will not start;
- poor engine performance;
- knock during acceleration;
- Engine misfire.
Fig.5 and fig.6 show the crankshaft cogwheel with a damaged damper. This failure makes proper synchronization of the phases of the injection and ignition impossible, since the inner part is shifted to the cogwheel and therefore the phases of the injection and ignition are shifted to one another.
Fig. 5 Fig. 6
Procedure for checking the condition of CKP
- Perform an external visual inspection of the CKP and the crankshaft cogwheel.
- Check the CKP harness for corrosion and damages.
- Make sure harness pins are tight in their places and there’s good electrical contact.
- Check that the air gap between the cogwheel and the CKP sensor is within the limits.
- Disconnect the sensor harness.
- Measure with ohmmeter the active resistance between the terminals of the CKP. Check the database what should be the value of measured resistance of the sensor for the corresponding brand and model of the car. If the reading shows extremely high resistance, this means that there is an open circuit in the sensor. Zero or close to zero indication means short circuit in the coil.
NOTE: Regardless of measured resistance is within acceptable limits, it can’t be taken as evidence that the CKP will be able to produce a correct signal.
Check the shielded CKP cable:
- CKP may have shielded cable (not in all cases). Strip the coupling of the harness.
- Connect one of the probes of ohmmeter to one of the terminals of the СКР (1 or 2).
- Connect the other probe to the terminal that corresponds to the shield. The reading should incline to infinite resistance.
- Move the probe from the shield terminal and connect it to the ground. The reading should incline to infinity.
Note: In some systems the CKP shield cable is connected to its feedback CKP cable to ground. In this case the ohmmeter will read short circuit, which will be normal for this system. Explore electrical circuit of the system you are testing to identify how exactly the CKP is connected.
- Plug in the sensor connector.
— Inductive type of sensor —
Connect the active end of the measuring probe to one of the terminals of the CKP and the other end to the ground. You will observe the picture as in fig. 7 - when the engine is cranking and in fig. 8 - when the engine is idling.
Pay attention to the amplitudes of the electric pulses during engine cranking and during engine idling. In the first case the signal amplitude will be significantly lower.
Thus you can determine the performance of the CKP as well as the wear of the crankshaft cogwheel. An example representing cogwheel wear is shown in fig. 10. Fig.11 shows a high wear. You have to replace the crankshaft cogwheel in this case.
NOTE: CKP is polar sensor and exchange of signal terminals "Plus" and "Minus" is equivalent to malfunction.
— Hall sensor —
The picture you have to observe in this case is as follows (fig. 12).
Prolonged impulse marks the synchronization pulse and each of the other shows the tooth passing by the sensor.