DTC P0324: Knock Sensor Module Circuit: Description
WARNING: This page is about a different car, the 2001 Saturn LW300 and 2001 Saturn L300. However, it is still accessible from the selected car via links, so may be relevant.
ECM monitors a zero pulse and a test pulse from knock sensors to assure it can still detect knock. This diagnostic runs once per 255 engine cycles after vehicle is operating in closed loop. This code indicates an error in knock switch or knock evaluation circuit, both internal to ECM.