Knock Sensor
The Knock Sensor (KS) is a piezoelectric device which detects abnormal engine vibrations (spark knock) in the engine. This vibration results in the production of a very low AC signal, which is sent from the KS to the KS module (integral to ECM). The ECM then retards ignition timing until the engine knock ceases.
A fault in the KS circuit may set a DTC. See SELF-DIAGNOSTICS - 2.2L VUE or SELF-DIAGNOSTICS - 3.0L VUE article.