Most likely, your ECU is never seeing a knock signal from the sensor. This is a fault as it should show at least a little ping under hard acceleration. Since it sees no knock, it assumes the sensor is bad an retards the timing to be safe. The first place to start is to probe the wiring from the sensors to the ECU to see if there is possible a broken or grounded lead. If the wiring checks out, you need to check the sensors themselves. The check procedure in the book calls for a scope to see the waveforms. I don't have my books available, so hopefully someone else can help you with the location of the sensors. There should be one in each bank, I think they are either in the side of the block just under the head, or they could be in the "V" under the intake. On most engines, they locate the knock sensor as close as possible to the deck surface. If it has a code for each bank, you may be able to swap the sensors and see if it then gives the code for the other bank.
Gary M.