Knock Sensor: Description and Operation

DESCRIPTION
The knock censor circuit consists of a knock sensor, circuit 496 and the PCM. The sensor is mounted in the back of the engine near the top of the block and is used to detect abnormal vibration (spark knocking). Within the engine block, the sensor produces an A/C output voltage which increases with the severity of the knock. The PCM will retard timing to a maximum correction based on the signal it receives from the knock sensor.

OPERATION
The PCM will learn a minimum noise level at idle from the knock sensor and compare level at around 1500-3500 rpm. If the PCM sees no change in noise a DTC P0327 will set after an elapsed time. If the PCM cannot control knock whereas the sensor has detected too much noise due to an excessively noisy engine, a DTC P0326 will set.

The PCM will automatically retard spark to a value that corrected a knock problem previously if it exists again in that ignition cycle. The PCM however, will always try to work back to a zero compensation or no retard.

The knock sensor signal is only used during the TDC combustion event, which is determined by the 7x signal (knock window).