Circuit/System Description

The knock sensor (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, the KS frequency changes. This signals the powertrain control module (PCM) to retard ignition timing. The PCM sends a bias voltage of 5 volts to the KS on the KS Signal High circuit. The PCM expects approximately 2.5 volts back on the KS Signal Low circuit. The KS generated AC signal rides on top of the bias voltage provided by the PCM. The circuits between the KS sensor and the PCM consist of the following circuits:

• A KS signal
• A low reference
• A shielded ground