Knock sensors detect abnormal vibration in the engine and are designed to reduce spark knock during heavy detonation, allowing for maximum spark advance to enhance driveability. These sensors produce AC output voltage that increases with the severity of the knock, sending a signal to the PCM to retard timing in response to detonation. Knock sensors are utilized in various models, including Civics with D16Y5, D16Y8, and B16A2 engines, as well as Integras with B18C1 and B18C5 engines, and all CR-V models. To check a knock sensor, disconnect the electrical connector and unscrew it from the engine, then reconnect the wiring harness. Using a voltmeter set to the lowest AC voltage scale, connect the negative probe to the sensor body and the positive probe to the sensor terminal. Gently tapping the bottom of the sensor simulates engine knock, allowing for observation of voltage fluctuations; if none are detected, the sensor should be replaced. When replacing the sensor, coolant will drain from the block, so it is necessary to drain the cooling system and place a drain pan underneath. After disconnecting the electrical connector and unscrewing the sensor, install the new sensor, which comes precoated with thread sealant, without adding more sealant to avoid operational issues. Tighten the sensor to the specified torque without overtightening, reconnect the electrical connector, refill the cooling system, and check for leaks.