According to the Bentley (pp. 28a-6-7), here's the procedure:
1. Remove the knock sensor from the cylinder block and disconnect
the 3-pin connector.
2. Using the knock sensor mounting bolt, a washer, and a nut, tighten
the bolt through the knock sensor to the specified torque [i.e. 20 Nm
(= 15 ft-lb)].
3. Connect a voltmeter (DC volts) to terminals 1 and 2 in the connector
[i.e. the two terminals on the left, facing the sensor].
4. Using a metal object, lightly tap on the mounting bolt. The
voltmeter should register small fluctuating amounts of voltage. Voltage
will vary based on the intensity of the tapping.
5. If any faults are found the sensor is faulty and should be replaced.