From what I got told the knock sensors are a one time trip thing, once it detects knock it pulls the EML up and trips the sensor. Only way to get it to go off is to replace it, and that the knock sensor has no bearing on the ecu in closed loop, its just a fail safe. How true that is I don't know though. I'm guessing chances are you probably have a wiring fault, you would be able to hear if its knocking or not.