Circuit Description
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The DTC P0325 Knock Sensor (KS) Circuit diagnostic monitors activity on the knock sensor circuit. The KS is non-resonant design that is constructed of a piezoelectric element which generates an AC signal when vibrated. Normal engine operation will cause the KS to generate signals of known frequencies. When engine knock is present, KS frequency changes. This signals the Powertrain Control Module (PCM) to retard ignition timing. PCM sends a bias voltage of 5 volts to the KS on KS signal high circuit. PCM expects approximately 2.5 volts back on KS signal low circuit. KS generated AC signal rides on top of bias voltage provided by the PCM.