Detonation is a phenomenon in which the air-fuel mixture spontaneously ignites. The crankshaft of the engine continues to rotate, experiencing tremendous loads. In order to get rid of it, it is necessary to timely correct the moment of fuel injection, ignition. In modern injection cars, electronic control systems are used on microcontrollers. They allow you to take off a lot of characteristics and control the operation of all components and assemblies.
Knock Sensor Device
In any knock sensors (VAZ, GAZ, foreign cars) a piezoelectric element is used. The bottom line is that when this element is exposed, a signal is generated. And the greater the load, the stronger the signal level. Detonation is a knock, in fact. Therefore, if you hit something on the body of the sensor, it will generate a signal of a certain magnitude. The following types of sensors are used on modern internal combustion engines:
- Broadband (with two contacts).
- Resonant (with one contact).
It is on these features that two types of devices are distinguished.
How the sensor works
The VAZ knock sensor is located, regardless of its type, between the second and third engine cylinders - this is where the middle of the block is located. Therefore, the device equally detects detonation in the first and fourth cylinders (the distance from them to the sensor is the same). Knocking is a phenomenon that can harm pistons, rings, fingers, valves. And with prolonged exposure, the engine will simply fail.
When the sensor picks up the detonation, it sends a corresponding signal to the electronic control unit. The latter analyzes the signal level and adjusts the ignition timing, the moment of fuel injection, etc. These characteristics also depend on the quality of the fuel mixture (this parameter is controlled by an oxygen sensor).
Varieties of sensors
In the early years of production on Lada injection cars, exclusively resonant ones were installed. The peculiarity of single-contact sensors is that they are able to catch only knocks of the detonation frequency. But broadband devices perceive all noise bands, after which it detonates. Both types of devices work differently; just replacing one with the other will not work. Even if you replace the wiring (because the number of conclusions is different), this will not solve the problem. And if you decide to install a broadband sensor, you will have to change the electronic control unit, designed to work with it.
Product Cost
On sale you can find many products from different manufacturers. And if there is a malfunction of the knock sensor, it should be replaced. The cost of some is very high, but for domestic cars you can use cheap appliances. Resonant knock sensors manufactured by General Motors will cost about 2500-2700 rubles.
Not cheap, but the broadband devices of the domestic manufacturer AvtoPribor cost 250-350 rubles, and StartVolt is about half the price - about 200 rubles. The price of the electronic control unit in the secondary market is 2000-3000 rubles. Consequently, it will be much easier to remake the entire system for the use of broadband cheap sensors than to install imported single-contact ones.
The main symptoms of knock sensor failure
If we talk about cars of domestic production of VAZ, then the knock sensor malfunctions are manifested as follows:
- On the dashboard, a lamp lights up, indicating a breakdown in the engine systems.
- A noticeable deterioration in the dynamics of the car, there is a lack of power.
- If you sharply press the gas pedal, a knock will appear, signaling detonation.
- Increase engine operating temperature. The piezoelectric element does not work, as a result of which the electronic control unit sets an incorrect ignition timing.
The most common causes of detonation are low-quality gasoline and motor overheating. But at the same time, the sensor should work and send an appropriate signal to the computer, which will correct the angle and allow you to get rid of the knock.
Engine Error Codes
In the event that there are symptoms of damage to the DD and the Check Engine lamp starts to light, check the engine with a scanner. Signs of detonation usually occur with the following errors:
- P0326 - high signal from the sensor.
- P0327 - An excessively low sensor signal.
- P0325 - open circuit to the knock sensor.
Please note that error 0327 can signal not only a failed knock sensor, but also that there is a poor-quality contact in its connection circuit. Check all connections, if necessary, clean and treat with penetrating grease. Oxidized contacts are a very common cause of this error. The main reasons why code 0327 appears:
- Device malfunction.
- No power or control signal to the knock sensor connection block.
- There is rust in the place where the instrument housing is attached to the engine block.
If the case is rusted or oxidized, then it can be cleaned with sandpaper. But if there is a lot of pollution, it is easier to replace the device - the cost of a broadband device is small.
Diagnostics
In the place where the knock sensor is located, the level of knocks of the same size will cause an equal effect on the engine block. Therefore, the DD will generate the same level signal. To check the operability of the device, you must:
- Set the multimeter to voltage measurement mode (0.2 V).
- Connect the contacts of the device with the probes of the multimeter.
- Gently apply a few strokes to the sensor body - so you can make an imitation of detonation knocks.
- Look at the readings of the multimeter - they should change.
Detonation is a knock, and short-term. Therefore, it is advisable to use not a digital multimeter for diagnostics, but a pointer one - it will much more clearly show the operation of the device. To replace the sensor, you will need to disconnect the old one from the block, unscrew the fastening nut and remove the old one. A new one is installed in its place and the nut is tightened. Having connected a block of wires, it is necessary to check the operability of the system.