Knock Sensor (KS)

Fig. 1 Knock Sensors:

Diagnostic Codes:
P0326, P0327, P0328, P0331, P0332, P0333

Monitoring Procedure
Knock sensing faults are detected by using two tests. If the knock controller cannot adjust the background noise average to within limits then a knock sensor fault event is recorded and when the fault event counter reaches its limit, a low or high background noise knock fault is registered. If knock correction is at the maximum value for a set number of cycles then a continuous knock fault is registered.

The strategy will report to the Diagnostic Status Manager (DSM) when a knock sensing fault is present and the DSM will then decide whether to store a fault code and illuminate the MIL Lamp.

The knock sensor uses a piezo-electric sensing element to detect broad band (2-20 kHz) engine accelerations. When the closed loop knock controller is unable to adjust the background noise average to within a defined band either side of the reference background noise average then a fault has occurred, and a relevant fault counter incremented.

Fig. 1 Interface Between ECM & Knock Sensor:

Interface Between ECM And Knock Sensor (KS)

KS Circuit Range/Performance
KS 1 Circuit Range/Performance A,B - P0326
KS 2 Circuit Range / Performance A,B - P0331

When continuous knock detection on one or more cylinders has caused knock correction to reach it's maximum value and stay there for a predetermined number of cycles, then there is a knock sensor circuit range /performance fault.

Possible causes:
- Cylinder head overheats - loss of coolant
- Wrong fuel type used - low octane
- Cylinder deposits (on bank A,B)
- Quiet engine with background noise spikes causing retard A,B
- Radio Frequency Interference (RFI) affects knock signal - shielding problem with harness A,B
- ECM fault - knock ASIC fails

KS Circuit Low Input
KS 1 Circuit Low Input A,B - P0327
KS 2 Circuit Low Input A,B - P0332

When the closed loop knock controller is unable to adjust the background noise average to within a defined band either side of the reference background noise, then a knock sensor fault event has occurred. If the knock fault event counter reaches a given threshold, then a low or high background noise knock fault is present.

Possible causes:
- Knock sensor A,B not in good acoustic contact with block e.g. loose
- Knock sensor wiring open circuit or short circuit to ground
- Background anomalously quiet for a cylinder on that bank
- Knock sensor signal attenuated - harness problem
- Knock sensor fault A,B, lost sensitivity
- ECM fault - knock ASIC failed

KS Circuit High Input
KS 1 Circuit High Input - P0328
KS 2 Circuit High Input - P O333

When the closed loop knock controller is unable to adjust the background noise average to within a defined band either side of the reference background noise, then a knock sensor fault event has occurred. If the knock fault event counter reaches a given threshold, then a low or high background noise knock fault is present.

Possible causes:
- Background anomalously noisy for a cylinder on that bank
- Radio Frequency Interference adds to knock signal - harness shielding problem
- Knock sensor A,B - over sensitive
- ECM fault - knock ASIC failed

Additional Information
Knock sensors use a piezo-electric sensing element to detect broad band (2 kHz to 20 kHz) engine accelerations.

Output of sensor:
Charge sensitivity = 37.5 pC/g nominal
Voltage sensitivity = 29 + 15 % mV/g