knock sensor

“Knocking” occurs when the air-fuel mixture self-ignites prematurely. Sustained knocking causes damage primarily to the cylinder head gasket and cylinder head. The knock sensor identifies the high-frequency engine vibrations characteristic of knocking and transmits a signal to the ECU. The aim is to obtain the maximum energy yield by starting ignition as early as possible. Engines with a knock sensor can reduce fuel consumption and increase torque.

What is knock sensor?

The knock sensor monitors the combustion process in the engine. Its signal helps the engine control to prevent knocking combustion and therefore protect the motor/engine control. On this page we will provide you with various information, including how a defective knock sensor becomes noticeable, the causes that may lead to its failure, and how it can be tested in the workshop.

Important safety note The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their work. The information provided on this website is intended for use by suitably qualified personnel only.

The knock sensor is located on the outside of the engine block. It is intended to record knocking noise in all engine operating states in order to prevent engine damage.

 Car knock sensor function

The knock sensor "listens out for" the structure-borne vibrations from the engine block and converts these into electrical voltage signals. The signals are filtered and evaluated in the control unit. The knocking signal is assigned to respective cylinder. If knocking occurs, the ignition signal for the respective cylinder is adjusted in the "late" direction until knocking combustion no longer occurs.