Knock Sensor Operation

In conjunction with the ignition system, a knock sensor retard system is used. System consists of a knock sensor, knock sensor module (if equipped) and PCM. When detonation (engine knock) occurs, knock sensor produces a low voltage AC signal. This signal inputs to the PROM or knock sensor module (if equipped) located internal of PCM.

PCM supplies a 5-volt DC reference signal on the knock sensor signal line. Internal circuitry of the knock sensor will pull this voltage down to about 2.5 volts. When detonation (engine knock) occurs, the knock sensor produces an AC voltage signal which rides on the 2.5-volt DC signal back to the knock sensor module or PCM. The voltage and frequency of this signal depends upon knock signals received by the knock sensor. The PCM will retard ignition control timing until signals from knock sensor cease.

Failure in knock sensor circuit should set a related diagnostic trouble code. If a related diagnostic trouble code is not present and the knock sensor system is suspected as the cause of a driveability problem, perform a functional check of the knock sensor. See appropriate SYSTEM & COMPONENT TESTING article.