Knock Sensor — General Information (BMW X5 E53)

The knock sensor is positioned in a location that provides optimal knock detection in all engine cylinders. The vibrations of the engine block during knocking are transmitted to the ring piezoceramic disk, where it induces an alternating voltage and outputs it as a signal to the ECU via a shielded wire.

In this case, the ECU reduces the ignition advance angle in the corresponding cylinder by 4°. If detonation in this cylinder does not stop, the ignition advance angle is reduced in all cylinders. The maximum reduction in the ignition advance angle is 12°. After detonation stops, the ECU gradually increases the ignition advance angle until detonation occurs, and the regulation cycle is repeated.

When two or more sensors are installed, their operation is synchronized with the rotation of the camshafts, which allows for control of the ignition advance angle for each cylinder separately. Regulation is performed in steps, with an interval of 4°.

The use of this sensor allows maintaining the maximum permissible pressure in the engine combustion chamber on the verge of detonation combustion. Thus, ensuring efficient use of fuel with its minimum consumption. The detonation sensor records fluctuations during combustion and is directly connected to the ECU-KSUD. When detonation combustion occurs, the ignition timing is automatically set later.

If the sensor fails, the ECU sets the ignition timing so late as to prevent detonation combustion, which results in a loss of power, reduced efficiency, but the integrity of the engine is preserved. If one of the detonation sensors fails, the ECU automatically sets the ignition timing to the side of delay so that detonation combustion does not occur in the engine.