The knock sensor monitors the combustion process in the engine. Its signal helps the engine control to prevent knocking combustion and therefore protect the motor/engine control. On this page we will provide you with various information, including how a defective knock sensor becomes noticeable, the causes that may lead to its failure, and how it can be tested in the workshop.
Check the wiring to the control unit by checking continuity and short circuit to frame for every wire to the control unit plug.
Connect the ohmmeter between the knock sensor connector and the removed control unit connector. Setpoint: <1 Ohm (circuit diagram required for the pin assignment of the control unit).
Check the respective pin at the wiring harness connector against ground using an ohmmeter and with the control unit connector removed. Setpoint: at least 30 MOhm.
Attention:
A connection pin can act as shielding and thus have continuity to ground.
Connect the test probes of the oscilloscope between the control unit pin for the knock sensor and ground.
The oscillogram must produce a signal with considerably enlarged amplitude.
If the signal is not clear, tap gently against the engine block near the sensor.
If the knocking is not detected, this indicates a defective sensor or circuit.
