Knock Sensor: Description and Operation

Knock Sensors

The specification for advance and retardation vary per engine.

In the case of engine knock, the ignition timing for the knocking cylinder(s) is retarded until knocking is no longer detected.

When the engine knocking disappears, the ignition timing will be advanced in small steps until the knocking occurs again, then retarded. This cycle is continually repeated.

Under certain conditions, knocking in multiple cylinders or significant knocking in a single cylinder can influence the timing in all cylinders.

Effect in the event of a signal failure

• In the event of failure of a knock sensor, the ignition timing for the relevant cylinders is retarded.

• In the event of failure of all knock sensors, the engine management switched to knock control emergency running, in which the ignition timing is generally retarded.

• Fuel engine power is no longer available.

• A failure of the Camshaft Position (CMP) sensor will NOT allow knock control.