Knock Sensor
The Knock Sensor (KS) is a piezoelectric device which detects abnormal engine vibrations (spark knock) in the engine. KS is located on side of engine block, above oil filter. See Fig 1 . This vibration results in the production of a very low AC signal, which is sent from the KS to the KS module (integral to PCM). The PCM then retards ignition timing until the engine knock ceases. Two KS are used on some models.
A fault in the KS circuit may set a DTC. See SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS article.