Knock Sensor: Description and Operation

Knock Sensor:

PURPOSE
The knock signal is generated by the knock sensor. When engine knock is detected, the knock sensor develops a voltage which the ignition ECM registers. This signal is then sent from the ignition ECM to the fuel injection ECM. The ECM's then take appropriate action by retarding the ignition timing and enriching the air/fuel mixture if necessary.

CONSTRUCTION
The knock sensor (C) consists of a housing (3) a piezoelectric crystal (4) mounted on a threaded sleeve (5) between two connector strips (6). One side of the assembly is fitted with a damping weight (7) and spring washer (8) secured by a nut (9).

OPERATION
Mounted on the engine block, the sensor is subjected to the vibrations generated by knock. The vibrations cause a small distortion on the surface of the piezoelectric crystal, which consequently generates a small voltage. This voltage is read by the ignition ECM.

SIGNAL
The signal from the sensor is a continuous, but variable voltage. The frequency of the voltage is dependent on the amount of engine knock. The signal is fed into the ignition ECM which computes it as a reference value. This reference value is then forwarded to the fuel injection ECM.