There are two knock sensors. It very unlikely that there will be differences from on e bank to the other. Therefore one sensor could be safely disconnected and the output monitored to ascertain exactly what is going on. A resistor of approximately 550K ohms as a substitute, should prevent an error code.
Unless the car is on a dyno it will be difficult to check sensor output using a scope. Being from a number 8 wire background I have a suggestion.
The manuals show an output impedance of 560k ohms, so that if the sensor output was hooked into the input of an audio amplifier, any signal occurring could will be audible, even if only as a series of clicks or thumps. Any sort of simple portable audio amp. or something incorporating same will do the trick.
The gain available will surely far exceed what is required, so that a 500k potentiometer should be connected across the sensor output, and the amp. fed from the wiper. A low gain input should be used if one is available. Audio fanatics will know what I have in mind.
Obviously I am suggesting an experiment with no guarantees.
