Circuit Description

Knock sensor produces an output voltage (AC) based on mechanical engine vibration. PCM will retard the electronic spark timing on the signal being received. The amplitude and signal frequency is dependent upon the knock level. Upon diagnosis of the sensor circuit, PCM will learn a minimum engine noise level at idle and compare to a noise level at around 2000-3000 RPM. This change does not necessarily mean spark knock is detected, but the sensor is giving the PCM a voltage signal based on the level of noise it sees. When PCM monitors the circuit, it will set a DTC if there is no change in output from the knock sensor between idle and 2000-3000 RPM.

DTC will set if there is an open or fault in the knock sensor circuit when the PCM has learned minimum noise level at idle for 5 seconds and does not detect a change in noise level between 2500-3500 RPM for 5 seconds, coolant temperature is greater than 149°F (65°C), engine run time is greater than 10 seconds or vehicle is moving to reach 2500-3500 RPM.