Knock Sensor: Description

The ECM uses active knock control, which serves to prevent engine damaging pre-ignition or detonation under all operating conditions enabling the engine to operate without additional safety margins. For the ECM to be able to determine the point at which a cylinder is pre-detonating, 2 piezo ceramic sensors are mounted on the engine block. Each sensor monitors all 4 cylinders in a bank (i.e. cylinders 1, 3, 5 & 7, and cylinders 2, 4, 6 and 8) by converting the engine block noise into a suitable electrical signal, which is then transmitted back to the ECM via a shielded cable. The signal is then processed within the ECM to identify the data that characterizes knocking. For knock sensor testing, see Fig 1 .

There are three knock sensor diagnostic checks during which a fault is detected if:

1. The sensor signal is less than the minimum engine RPM dependent threshold.
2. The sensor signal is greater than the maximum engine RPM dependent threshold.
3. The error counter for the verification of knock internal circuitry is exceeded.

Fig 1: Knock Sensor DTC Testing

Courtesy of LAND ROVER NORTH AMERICA, INC.