Knock Sensor

The knock sensor is located under the intake manifold, near the starter motor. The knock sensor detects abnormal vibration (spark knock or detonation) in the engine. The sensor produces an Alternating Current (AC) voltage which increases with the severity of the knock. The knock sensor is specifically tuned to the engine based on the frequency of vibration that the engine creates when it knocks. The knock sensor for the 4.6L Northstar is tuned to 7000 hertz. This signal is an input to the PCM, which then adjusts spark advance to reduce the spark knock.