Circuit Description
WARNING: This page is about a different car, the 1995 Oldsmobile Ninety-Eight and 1995 Buick Park Avenue. However, it is still accessible from the selected car via links, so may be relevant.
Knock sensor is used to detect engine detonation and allow PCM to retard Ignition Control (IC) timing based on signal being received. Circuitry within knock sensor causes PCM's supplied 5 volts signal to be pulled down, so that under a no knock condition circuit would measure about 2.5 volts DC. Knock sensor produces an AC signal which rides on 2.5 volts DC voltage. Amplitude and signal frequency is dependent upon knock level.
If circuit becomes open or shorted to ground, voltage will either become greater than 3.5 volts or less than 1.5 volts respectively.