The knock control system is designed to reduce spark knock during heavy detonation, allowing the engine to utilize optimal spark advance for improved driveability. The knock sensor detects abnormal engine vibrations and produces a voltage output that increases with the severity of the knock, which is monitored by the PCM to retard ignition timing until detonation ceases. In four-cylinder engines, the knock sensor is located on the backside of the engine block, directly below the cylinder head, while V6 engines have two knock sensors located underneath the intake manifold, one for each cylinder bank. To begin, disconnect the cable from the negative terminal of the battery, and if working on a V6 engine, drain the cooling system. For four-cylinder engines, pinch off the coolant hoses to the throttle body before removing the intake manifold/throttle body. After removing the intake manifold, disconnect the electrical connector and remove the knock sensor; for V6 engines, the sensors are under the intake manifold, while for four-cylinder engines, the sensor is screwed into the side of the block below the intake manifold. If reusing the old sensor, coat the threads with thread sealant, but do not apply additional sealant to new sensors as they are pre-coated. Install the knock sensor securely, tightening it to approximately 30 ft-lbs without overtightening to avoid damage. Finally, plug in the electrical connector, refill the cooling system, and check for leaks, ensuring that on 3MZ V6 models, the knock sensors are turned so the connector ends point toward the timing belt end of the engine for easier harness hookup.