Camshaft sensor malfunction symptoms
Content
What is a camshaft sensor for?
The functioning of the power unit in modern cars is controlled by electronics. The ECU (electronic control unit) generates control pulses based on the analysis of signals from numerous sensors. Sensors placed in different places make it possible for the ECU to assess the state of the engine at any given time and quickly correct certain parameters.
Among these sensors is the camshaft position sensor (DPRV). Its signal allows you to synchronize the operation of the injection system of a combustible mixture into the engine cylinders.
In the vast majority of injection engines, distributed sequential (phased) injection of the mixture is used. At the same time, the ECU opens each nozzle in turn, ensuring that the air-fuel mixture enters the cylinders just before the intake stroke. Phasing, that is, the correct sequence and the right moment for opening the nozzles, just provides the DPRV, which is why it is often called a phase sensor.
The normal operation of the injection system allows you to achieve optimal combustion of the combustible mixture, increase engine power and avoid unnecessary fuel consumption.
The device and types of camshaft position sensors
In cars, you can find three types of phase sensors:
- based on the Hall effect;
- induction;
- optical.
The American physicist Edwin Hall discovered in 1879 that if a conductor connected to a direct current source is placed in a magnetic field, then a transverse potential difference arises in this conductor.
The DPRV, which uses this phenomenon, is usually called the Hall sensor. The body of the device contains a permanent magnet, a magnetic circuit and a microcircuit with a sensitive element. A supply voltage is supplied to the device (usually 12 V from a battery or 5 V from a separate stabilizer). A signal is taken from the output of the operational amplifier located in the microcircuit, which is fed to the computer.
The design of the Hall sensor can be slotted
and end
In the first case, the teeth of the camshaft reference disk pass through the sensor slot, in the second case, in front of the end face.
As long as the lines of force of the magnetic field do not overlap with the metal of the teeth, there is some voltage on the sensitive element, and there is no signal at the output of the DPRV. But at the moment when the benchmark crosses the magnetic field lines, the voltage on the sensitive element disappears, and at the output of the device the signal increases almost to the value of the supply voltage.
With slotted devices, a setting disk is usually used, which has an air gap. When this gap passes through the magnetic field of the sensor, a control pulse is generated.
Together with the end device, as a rule, a toothed disk is used.
The reference disk and the phase sensor are installed in such a way that the control pulse is sent to the ECU at the moment the piston of the 1st cylinder passes through the top dead center (TDC), that is, at the beginning of a new unit operation cycle. In diesel engines, the formation of pulses usually occurs for each cylinder separately.
It is the Hall sensor that is most often used as a DPRV. However, you can often find an induction-type sensor, in which there is also a permanent magnet, and an inductance coil is wound over the magnetized core. The magnetic field changing during the passage of the reference points creates electrical impulses in the coil.
Optical-type devices use an optocoupler, and control pulses are formed when the optical connection between the LED and the photodiode is interrupted when the reference points are passed. Optical DPRVs have not yet found wide application in the automotive industry, although they can be found in some models.
What symptoms indicate a malfunction of the DPRV
The phase sensor provides the optimal mode for supplying the air-fuel mixture to the cylinders together with the crankshaft position sensor (DPKV). If the phase sensor stops working, the control unit puts the power unit into emergency mode, when injection is carried out in pairs-parallel based on the DPKV signal. In this case, two nozzles open at the same time, one on the intake stroke, the other on the exhaust stroke. With this mode of operation of the unit, fuel consumption increases markedly. Therefore, excessive fuel consumption is one of the main signs of a camshaft sensor malfunction.
In addition to the increased voracity of the engine, other symptoms can also indicate problems with the DPRV:
- unstable, intermittent, motor operation;
- difficulty starting the engine, regardless of the degree of its warming up;
- increased heating of the motor, as evidenced by an increase in the temperature of the coolant compared to normal operation;
- the CHECK ENGINE indicator lights up on the dashboard, and the on-board computer issues the corresponding error code.
Why DPRV fails and how to check it
The camshaft position sensor may not work for several reasons.
- First of all, inspect the device and make sure there is no mechanical damage.
- Incorrect DPRV readings can be caused by too large a gap between the end face of the sensor and the setting disk. Therefore, check whether the sensor sits tightly in its seat and does not hang out due to a poorly tightened mounting bolt.
- Having previously removed the terminal from the negative of the battery, disconnect the sensor connector and see if there is dirt or water in it, if the contacts are oxidized. Check the integrity of the wires. Sometimes they rot at the soldering point to the connector pins, so tug them a little to check.
After connecting the battery and turning on the ignition, make sure that there is voltage on the chip between the extreme contacts. The presence of power supply is necessary for the Hall sensor (with a three-pin chip), but if the DPRV is of the induction type (two-pin chip), then it does not need power. - Inside the device itself, a short circuit or open circuit is possible; a microcircuit may burn out in the Hall sensor. This happens due to overheating or unstable power supply.
- The phase sensor may also not work due to damage to the master (reference) disk.
To check the operation of the DPRV, remove it from its seat. Power must be supplied to the Hall sensor (the chip is inserted, the battery is connected, the ignition is on). You will need a multimeter in DC voltage measurement mode at a limit of about 30 volts. Better yet, use an oscilloscope.
Insert the probes of the measuring device with sharp tips (needles) into the connector by connecting them to pin 1 (common wire) and pin 2 (signal wire). The meter should detect the supply voltage. Bring a metal object, for example, to the end or slot of the device. The voltage should drop to almost zero.
In a similar way, you can check the induction sensor, only the voltage changes in it will be somewhat different. The induction-type DPRV does not require power, so it can be completely removed for testing.
If the sensor does not react in any way to the approach of a metal object, then it is faulty and must be replaced. It is not suitable for repair.
In different car models, DPRVs of different types and designs can be used, in addition, they can be designed for different supply voltages. In order not to be mistaken, purchase a new sensor with the same markings as on the device being replaced.
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