Operation CHARM: Car repair manuals for everyone.

Knock Sensor: Testing and Inspection

Knock Sensor:




A knock sensor with piezoelectric element (ceramic) is attached to the center of cylinder block of each bank #1/#2 to sense the engine knocking condition (Check for knocking for each cylinder).

The piezoelectric device output (V) = Q/C = 2dF/C (d = piezoelectric integer, C = Electrostatic capacity).

The ignition timing for MBT, Minimum spark advance for best torque, is located at the positions front and rear to the knocking limit and the ECM performs the control to make the engine to operate in optimum condition before the knocking limit.

Circuit Diagram:




When the knock sensor malfunctions, the ignition timing is corrected by the MAP values such as engine rate, air flow and engine coolant temperature, etc.

Troubleshooting hints
1. The MIL is ON or the DTC is displayed on the HI-SCAN under following condition.
- The knock sensor signal is not detected when the engine is in overload condition.
2. The knock sensor signal is abnormally low.

Harness Inspection Procedures: