The knock sensor is located on the engine block, cylinder head or intake manifold. This is because its function is to sense vibrations caused by engine knock or detonation. The PCM uses this signal to alter the ignition timing and prevent detonation. It will compare this information with its preset tables to identify a valid knock or ping. If a ping is sensed, it will retard the ignition timing to protect the engine from this damaging pre-ignition. Some important information for selecting the correct knock sensor is the type of sensor needed; sensor type, shape and size, number of connectors and poles, fitment position and date limitation of the unit. As car manufacturers regularly update certain peripherals and design of their models, some sensors will only be suitable for particular models of certain years.