I reading about the design of the knock sensor input circuitry,a short to battery,short to ground,or open circuit all result is a low knock signal voltage output,this output voltage is compared to a noise signal threshold (function of engine rpm and load)to determine knock sensor circuit high,circuit low or performance faults,some PCM/ECM modules use a driver circuit that will periodically and actively test the knock sensors lines for short circuit faults,in these modules supplemental codes can be set for the short circuit condition ,some PCM/ECM modules use standalone knock IC,in these modules the knock signal processing chip SPI bus is checked for proper communication between the main processor and the chip used as the interface the knock sensor,would also check for any codes set and monitor the high (knock retard)with obd scanner as SHOdded mentioned above,personaly have the MX obd bluetooth adapter along with torque pro which really comes in handy to monitor your vehicles functions,the above is a brief description of the sensors primary function,due apologize for the lengthy post on this topic just sometimes get in the mood to read and learn more about our vehicles aspects and all and before taking it to our local friendly dealer which most of us hate. Z
