The first thing to do is disconnect your battery for 30 minutes to clear the code, and while you're waiting, make sure the knock sensor is connected. If it comes back, make sure the threads on the sensor are clean and free of rust or grime. That situation can prevent it from detecting knock.
With ECT temp about 67° at idle, KR should be between 4 and 20°.
With the ignition on, disconnect the sensor and measure from the sensor harness to ground (use a DVM). It should be 4-6 VDC. If it isn't, you have a wiring problem.
The resistance of the sensor itself should be between 3.3k and 4.5k. Measure from the sensor terminal to a good ground location on the block. If it'* not, replace the sensor.