DTC P0326: Knock Sensor System Performance: Description

Knock sensor is a piezoelectric device that produces an AC voltage of different amplitude and frequency based on engine mechanical vibration. Amplitude and frequency are dependent on level of mechanical vibration knock sensor detects. PCM learns a minimum noise level at idle from knock sensor and uses stored normal noise level calibration values for the rest of the RPM band. Knock sensor signal is only used during top dead center combustion event of firing cylinder. When in a combustion event, PCM filters knock signal and compares it to normal calibration noise level for that RPM. If PCM has determined that knock is present during combustion event, it will retard timing on next firing cylinders until knock is eliminated. PCM will always try to work back to a zero compensation level, or no spark retard. DTC sets when PCM cannot eliminate spark knock by retarding spark timing, which most likely is caused by engine noise.