A knock sensor is a device that detects or senses any unusual vibration or knocking sounds in the engine caused by pre-ignition or detonation. It sends a signal to the engine control module (ECM) to adjust the timing and prevent engine damage. If a diagnostic test shows that the knock sensor is faulty or if you notice any issues with the engine’s performance such as loss of power, poor acceleration, or abnormal sounds, then it may need to be replaced.