Knock Sensor

Knock Sensor Description

1. Fault Codes:
P0326 Continuous knock detected, bank A
P0327 Knock background noise low, bank A
P0328 Knock background noise high, bank A
P0331 Continuous knock detected, bank B
P0332 Knock background noise low, bank B
P0333 Knock background noise high, bank B

The knock sensor is a 'Piezo-electric accelerometer' producing an output voltage proportional to mechanical vibration produced by the engine.
The ECM receives the signal, filters out any noise and calculates if the engine is knocking.
- Due to the cam and crank signals supplying information regarding the position of the engine in its cycle, the ECM can work out exactly which cylinder is knocking and will retard the ignition, within limits, on that particular cylinder until the knock disappears.
- It then advances the ignition again to find the optimum ignition point for that cylinder at that situation (i.e. fuel type, air temperature etc).
The ECM is able to adjust each cylinder timing for knock independently so all eight cylinders could have different advance angles all at the same time.

When the knock control is unable to adjust the background noise average to within a predefined band over a certain time, then a low or high background noise knock fault is present.

If one or more cylinders has reached its maximum knock correction value and stays there for a certain time i.e. continuous knock, then a continuous knock fault is present.

N.B. If the cam sensor fails, then knock control will be disabled.