Knock sensor. Principle of operation and verification

Modern cars are equipped with various sensors, on the basis of which the control unit regulates the operation of the whole unit. One of the similar elements involved in the fuel injection system is the detonation sensor, whose operation principle is based on the piezoelectric effect.

The detonation sensor is located on the engine of the car. It generates voltage pulses from detonation explosions in the engine. Based on the readings received from him, the control unit monitors the fuel supply, thereby achieving maximum engine power and fuel economy.

Types of knock sensors

There are two versions of this device - broadband and resonant. But now the resonant knock sensor is no longer installed serially. Also, you should know that they are not interchangeable, so to install, for example, instead of broadband resonance will not work.

Operating principle

The operation of the sensor is based on the piezoelectric effect. The controller sends a DC signal with a voltage of 5V to the sensor. It has a resistor that reduces the voltage to 2.5V and returns the AC signal to the controller. Transmission of the return signal is carried out along the circuit of obtaining the reference voltage. This is possible for the reason that the signal from the controller comes in the form of a direct current voltage, and the reverse signal is supplied by an alternating current voltage. In the event of a detonation explosion in the engine, the sensor generates an alternating current signal whose amplitude and frequency directly depend on the detonation force. If, during normal operation of the motor, an AC signal with a voltage of 2.5 V is returned to the controller, the controller leaves the engine running in the current mode. If the received signal has deviations from the set value, the controller changes the ignition timing to stop the detonation and to switch the engine to an economical and safe mode.

Checking the knock sensor

At home, the knock sensor and its operability can be checked with a multimeter. First of all, it is necessary to disconnect the electrical shoe from it, and then unscrew it from the engine. Connect the tester to the sensor as follows: the red (plus) wire is connected to the connector in the connector, and the black (negative) wire is connected to the housing. To test the operation, it is necessary to slightly tap on the thread, as a result of which the knock sensor should produce voltage pulses of up to 300 mV, which the multimeter registers. If the voltage surges are not recorded, the sensor is defective. If the multimeter catches the voltage after each stroke, then it is necessary to check the sensor and wire connectors. Very often it is in poor contact that the controller and sensor are not connected, so you need to clean the contacts. It is also necessary to check the wiring for an open circuit. It is possible that the cable just rubbed off somewhere or broke.