For knock protection, the Series 60 natural gas engines are equipped with a Knock Sensor and Signal Noise Enhancement Filter (SNEF) module. The knock sensor is located at the left rear of the cylinder head. The SNEF module is mounted on the left side of the cylinder block. The SNEF module receives electrical signals from the knock sensor and sends electrical signals to the ECM indicating knock level. The ECM uses this information to determine if the engine is knocking and adjusts ignition timing, air fuel ratio and throttle plate to protect the engine from excessive knock.