The knock sensor (KS) system enables the powertrain control module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The KS system uses two sensors. The sensors are located underneath the intake manifold. Each KS produces an AC signal that varies at all engine speeds and loads. The PCM makes adjustments to the spark timing based on the amplitude and frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM uses each KS to calculate the amount of normal engine noise, a noise channel, for a wide range of engine speeds and loads. The PCM compares the actual KS signal to the learned noise channel. When the PCM detects a KS signal that varies outside of the noise channel, the PCM will retard the spark timing until the knock goes away. If the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system, this DTC sets.

The PCM detects a malfunction in the integrated KS diagnostic circuitry that will not allow proper diagnosis of the KS system.