DTC P0325: Knock Sensor Module Circuit: Description
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
The Knock Sensor (KS) produces an AC voltage at all engine speeds and loads. Depending on the amplitude and frequency of the KS signal, the Powertrain Control Module (PCM) will adjust the spark timing. The PCM uses the KS signal in order to calculate the average voltage. The PCM inspects the KS and the related wiring by comparing the actual knock signal to the assigned voltage range. If the KS system is operating correctly, the PCM should monitor the KS voltage that is varying above and below a predetermined average voltage. This DTC will set if the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system.