Knock sensor

Definition

The knock sensor is a piezoelectric microphone bolted to the engine block that detects the high-frequency vibration of detonation (uncontrolled combustion). When the ECU sees knock it retards ignition timing for that cylinder and slowly advances again, allowing aggressive timing on good fuel without damaging pistons. A failed sensor, loose mounting bolt or corroded connector makes the ECU default to conservative timing, so the driver notices lost power and higher consumption but rarely a drivability fault. Mechanical noises such as a rattling heat shield, worn rod bearings or piston slap can be read as false knock. Codes: P0325-P0334; torque the sensor to spec (typically about 20 Nm), since over-tightening changes its resonance.

Codes often stored

• P0325Knock Sensor 1 Circuit Malfunction (Bank 1 or Single Sensor)
• P0326Knock Sensor 1 Circuit Range/Performance
• P0327Knock Sensor 1 Circuit Low
• P0328Knock Sensor 1 Circuit High Input (Bank 1 or Single Sensor)
• P0330Knock Sensor 2 Circuit (Bank 2)
• P0332Knock Sensor 2 Circuit Low Input (Bank 2)

Terms to know