Knock Sensor: Description and Operation

ESC Knock Sensor:

PURPOSE
The knock sensor sends an AC signal to the Electronic Control Module (ECM) when it detects engine detonation.

OPERATION
The knock sensor is mounted on the engine to detect engine detonation and the Electronic Control Module (ECM) will retard the electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 2.5 volts.

The knock sensor produces an AC signal which rides on the 2.5 volts DC voltage. The amplitude and signal frequency is dependent upon the knock level. If CKT 496 becomes open or shorted to ground, the voltage will either go above 3.5 volts or below 1.5 volts. If either of these conditions are met for about 1/2 second, a Code 43 will be stored.