The knock sensor 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 knock sensor to the ESC controller (some "C" and "K" series with 4.3L) or the control module (all others). The control module then retards ignition timing until the engine knock ceases. Two knock sensors are used on some models
Note. For additional information on knock sensor operation, see ESC DETONATION RETARD OPERATION under IGNITION TIMING CONTROL SYSTEMS .
A fault in the ESC circuit may set a related trouble code. When a related trouble code is not present and the ESC system is the suspected cause of a driveability problem, perform functional check of ESC system. See SYSTEM/COMPONENT TESTS - 4.3L article.