"Knocking" occurs when the air-fuel mixture self-ignites prematurely.Checked 2026-08-12
Engine knock and the knock sensor
Knock is the mixture igniting on its own; the knock sensor hears it so the computer can pull timing.
Also called: knock · detonation · pinging · knock sensor
What it means
Definition
Bosch, an OE sensor maker, defines the event: knocking occurs when the air-fuel mixture self-ignites prematurely, instead of burning from the spark. The same page describes the sensor's role — the knock sensor identifies the high-frequency engine vibrations characteristic of knocking and transmits a signal to the ECU. The computer then retards ignition timing until the knocking stops.
Why a buyer cares
What it changes
Because correction is automatic and silent, knock the driver can hear means the correction is no longer keeping up. A stored knock sensor code means the ear itself may be the fault.
In practice
Where you meet it
As a knock sensor code on a scan printout, and as a pinging noise under load on a test drive.
Two things that look alike
Not the same as
The sensor and the sound are not the same thing: a stored knock sensor code names the part that listens for knocking, not knocking itself.
Read next
Related terms
Diagnostic Trouble Code (DTC)
The code an OBD-II system stores to identify which monitored system it found a fault in.
Spark plugs and ignition coils
The parts that make and deliver the spark; on modern engines each plug has its own coil.
Intake valve carbon buildup
Deposits that accumulate on the back of the intake valves, most associated with direct-injection engines.
Where this comes from
Sources
The knock sensor identifies the high-frequency engine vibrations characteristic of knocking and transmits a signal to the ECU.Checked 2026-08-12
The entry does not separate knocking from pre-ignition. The Bosch quotes do not carry that distinction, and the only writing found that states it plainly is paid SAE conference material, so the sentence that drew it was cut rather than published under a citation that does not cover it.