Knock Sensor

Knock Sensor

The knock sensor is on the engine block, cylinder head, or intake manifold. It senses vibrations caused by engine knock or detonation. When the ECM receives this signal, it retards the ignition timing, averting harm to the engine.

Causes of engine knock or detonation

The knock sensor is a piezoelectric sensor that contains a sensing crystal and a resister. This crystal creates a small amount of voltage when shaken. This sensor takes advantage of this unique property.

Knock Sensor Symptoms

Laptop scannner for knock sensor code (P0325-P0332).

The symptoms of a bad knock sensor usually show up while accelerating or under a load. Be clear that this sensor affects the ignition timing of an engine. There will be a drop in fuel mileage and acceleration, especially at highway speeds. The customer may complain that the vehicle's engine doesn't feel right.

Some (COP) coil-over plug ignition systems use strategies that cancel cylinders; see the manufacturer's manual for special instructions. Often, these sensors are located on the cylinder heads under the intake manifold. When the vehicle's computer (ECM) detects a faulty knock sensor, it sets a code (P0325-P0332) and enters fail-safe mode.