This device listens for unusual engine vibration, shuts down the spark knock when detonation hits hard, and lets you take full advantage of better power delivery and better driving comfort. The Knock Sensor creates alternating current (AC) output voltage that shows PCM how bad the knock is, which then tells the PCM when to push back the spark timing. The four-cylinder models have the sensor placed on the engine block next to the intake manifold, while the V6 models put it in the middle underneath the intake manifold. To see if the sensor is working right, disconnect the wiring plug and measure the resistance between terminal 1 and a healthy ground using an ohmmeter; values around 500 to 620 KH should show up at 77° Fahrenheit. Replace the sensor when the resistance reading falls outside these two values. Follow these steps to put in a new sensor under the intake manifold on V6 engines: First, detach power to the old sensor, pull out the intake manifold, unplug its electrical wiring, unscrew the bolt that holds it, then pull out the sensor from the motor block. After installing the new sensor, reinstall everything backward.