Knock Sensor Monitoring
14. Knock Sensor Monitoring14.1.1. Knock Sensor and Knock Signal Diagnosis
The knock sensor bases on the piezo-electric principle. The engine noise is transformed into a voltage raw signal. The combustion noise is filtered out of this raw signal by a special knock-IC. The knock-IC, the sensor and the circuit are monitored by several monitors.
14.1.1.1. Knock-IC monitor (acquisition)
One monitor verifies the integrity of the knock-IC and the communication between the knock-IC and the main micro-processor.
14.1.1.2. Monitoring Conditions for knock-IC
- always on
14.1.1.3. Flowchart: Knock-IC monitor
14.1.1.4. Knock-signal basis value monitor
A properly working sensor typically measures a signal at a running engine even if no knocking occurs. Therefore the magnitude of deflection of the knock signal is verified by processing the absolute value in a mean value filter. If the mean value of the absolute knock value does not exceed a certain threshold the error counter for insufficient magnitude is incremented.
If the error counter exceeds a threshold the failure management is triggered and a DTC is stored.
14.1.1.6. Flowchart: Knock-signal basis value monitor
14.1.1.7. Knock-signal relative value monitor
The raw signal is typically not constant at a running engine even if no knocking occurs. If the absolute value of the difference between raw signal and filtered signal is below a certain threshold the error counter is incremented.
If the error counter exceeds a threshold the failure management is triggered and a DTC is stored.
14.1.1.8. Monitoring Conditions for relative value monitor
Knock control enabled
ECT > threshold
Mass air flow > threshold
Engine operation state: NOT deceleration or deceleration fuel cut
14.1.1.9. Flowchart: Knock-signal relative value monitor
