Operation

Knock Sensor (KS):

The Knock Sensor (KS) system has two major components.
^ The KS module part of the Powertrain Control Module (PCM).
^ The knock sensor (1).

The KS detects abnormal vibration (detonation) in the engine. The KS is located in the center of the engine block below the intake manifold. The KS module receives the KS signal and communicates within the PCM. After the correct calculations are made the PCM adjusts the ignition timing in order to reduce detonation.

When the KS detects detonation, the KS module opens a circuit in the PCM. In response the PCM retards the spark advance in order to reduce detonation. The amount of timing retard that the PCM applies is based on engine speed and the length of time that engine detonation is detected. Once the spark timing is retarded, the KS module performs calculations in order to determine whether more or less spark timing advance is required. Normally the ignition timing advance is increased until zero retard (normal ignition timing) is re-established. If detonation occurs again the whole cycle will repeat itself. The alteration of ignition timing by the KS often occurs continuously while the engine is running even though no detonation is heard by the vehicle's operator.

Results of Faulty Knock Sensor (KS) Operation
Loss of the knock sensor (KS) signal or loss of ground at the KS module causes the KS signal to the powertrain control module (PCM) to remain high. A constantly high input to the PCM from the KS causes the PCM to control the ignition timing as if no detonation were occurring. Failure of the PCM to retard ignition timing when necessary could cause any of the following concerns:
^ Excessive engine detonation
^ Engine damage during heavy engine loads
^ Higher exhaust emissions

A KS that falsely indicates detonation can cause the PCM to retard ignition timing unnecessarily. Reduced spark advance can cause any of the following conditions:
^ Poor fuel economy
^ Sluggish engine performance
^ Higher exhaust emissions