DTC P0325: Knock Sensor Module Circuit: Description
WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
Knock Sensor (KS) produces an AC voltage at all engine speeds and loads. Powertrain Control Module (PCM) then adjusts spark timing based on amplitude and frequency of KS signal. PCM uses KS signal to calculate average voltage. Then PCM assigns a voltage value. PCM checks KS and related wiring by comparing actual knock signal to assigned voltage range. A normal KS signal should stay within assigned voltage range. DTC P0325 will set if PCM malfunctions in a manner that will not allow proper diagnosis of KS system.