Circuit/System Description

The knock sensor is a piezoelectric device that produces an AC voltage of different amplitude and frequency depending on the level of engine mechanical vibration. The knock sensor system monitors the knock sensor in order to determine if detonation or spark knock is present. If the knock sensor system determines that excessive knock is present, the engine control module (ECM) retards the spark timing based on the signal from the knock sensor system. The knock sensor produces an AC signal when specific frequencies are detected. The ECM then retards the timing until knock is controlled.

The ECM tests the functionality of the internal knock sensor signal evaluation circuitry. The knock sensor circuitry within the ECM is responsible for receiving, amplifying, filtering, and evaluating the AC voltage and frequency from the knock sensors. The ECM performs two tests that determine if the internal circuitry within the ECM is functioning correctly.

Test One 

The ECM internally turns OFF the knock sensor signal circuits. The ECM then applies different test signals to the internal knock sensor circuitry to verify that each test signal output response is within range. If the ECM detects that any of the test signals are not within range, this DTC sets.

Test Two 

The ECM internally turns OFF the knock sensor signal circuits. The ECM then tests for any output response when no test signals are applied. If the ECM detects an output response, this DTC sets.

Test Three 

The ECM internally turns OFF the knock sensor signal circuits. The ECM generates an internal test pulse and monitors the return signal. If the return test pulse is less than a calibrated threshold, this DTC sets.