What does the engine knock sensor do?

The engine knock sensor detects abnormal combustion in the engine, specifically detonation (also called knocking or pinging). Detonation is a rapid, uncontrolled explosion of the air-fuel mixture in the combustion chamber, rather than the smooth, controlled burn desired. This is harmful to the engine.

When the knock sensor detects detonation, it sends a signal to the engine control unit (ECU). The ECU then adjusts the ignition timing, retarding (delaying) it to reduce the likelihood of further knocking. This helps protect the engine from damage caused by detonation. In some cases, it might also adjust the fuel mixture slightly.