The knock sensor is located on the engine block, cylinder head, or intake manifold. Its senses vibrations caused by engine knock or detonation. The PCM uses this signal to alter the ignition timing and prevent detonation. It compares this information with its preset tables to identify a valid knock or ping. If it senses ping, it retards the ignition timing to protect the engine from this damaging pre-ignition.
The knock sensor is a piezoelectric sensor that contains a piezoelectric sensing crystal and a resister. This crystal creates a small amount of voltage when shaken. This sensor takes advantage of this unique property.
Symptoms: 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 (PCM) detects a bad knock sensor, it sets a code (P0325-P0332) and enters fail-safe mode.