The knock sensor is attached to the cylinder block and senses engine knocking. The sensor contains a piezoelectric element that converts vibration (or noise) into voltage signal and sends this signal to ECM. With input signals from camshaft position and crankshaft position sensor, ECM can identify which cylinder is knocking. ECM filters vibrations and determines if the vibrations are knocking signal. The Engine Control Module (ECM) uses this signal to suppress knocking by retarding ignition timing. The ECM will set a code (Malfunction Indicator Lamp will Not turn on) if during two driving cycles the Knock sensor’s output voltage falls below minimum threshold. This code indicates an unexpected vibration is being read by the Knock sensor or ECM under normal engine operation.
The ECM monitors the range of the analog input signal from knock sensor to check sensor failure that is short circuit or open circuit. If the difference between knock signal and noise level is smaller than the threshold during defined time period, the DTC P0325 is set. In case the noise level is higher than the upper threshold or lower than the lower threshold, the DTC P0325 is set too.
Item
Detecting Condition
Possible Cause
DTC Strategy
? Plausibility check
? Open/short in signal or ground circuit
? Poor connection or damaged harness
? Faulty knock sensor
Enable Conditions
? Knock detection function active
? Engine rpm >2700 rpm
? Air mass >250mg/tdc.
? No relevant failure
Threshold Value
? Difference between the processed knock sensor signal and its mean does not exceed a threshold(0.08V) & the integral of the processed knock sensor signal does not reach the threshold(3V) for cylinders 2 and 3
? If the mean processed knock sensor signal of any one cylinder leaves the valid range(0.1V~4.5V).
Diagnostic Time
? 100 rev.