Knock Sensors

The use of knock sensors allows the ECM to constantly maintain the optimum ignition timing curve for all engine operating conditions. If detonation occurs, the signal from the sensors allows the ECM to retard the ignition timing to prevent engine damage. Each knock sensor produces a varying voltage signal (extremely low) that is dependent on the level of "vibration" noise produced by 1, 2 or 3 cylinders. By comparing the noise level at operating temperature to the level of noise during start/warm up the maximum timing advance can be reduced.

The ECM control module monitors detonation through two or four knock sensors (depending on the system) which are mounted as follows:
- In line four and six cylinder engines starting with the 1992 M42 and 1993 M50 TU. These engines utilize two sensors mounted on the intake side of the cylinder block.
- V8 M60 & M62 engines. These engines utilize four sensors, two per bank mounted in the "V" of the cylinder block.
- M73 engine has a total of four knock sensors but only two per ECM. In this case the knock sensors are mounted on the intake side of each cylinder head.