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Knock Sensor System Description

Knock Sensor System Description

Circuit/System Description

The knock sensor system enables the engine control module (ECM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The ECM uses the knock sensor system to detect abnormal engine sounds that can indicate detonation, also known as knocking.

Sensor Description

This knock sensor system uses one or two flat response dual-wire sensors. The sensor uses piezo-electric crystal technology that produces an alternating current (AC) voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency depend on the level of knocking that the knock sensor detects. The ECM receives the knock sensor signals through 2 isolated signal circuits.

If the ECM has determined that knocking is occurring, it will retard ignition timing to attempt to eliminate knocking. The ECM can control retardation of the ignition point individually for each cylinder. The ECM always tries to get back to the zero-compensation point, i.e. no ignition retardation. The knock sensor circuits are calibrated to detect errors in the knock sensor circuits in the ECM, the knock sensor harness, or the output voltage of the knock sensor. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive mechanical engine noise.