The Knock Sensor (KS) is used to monitor detonation in the combustion chamber. Detonation occurs when the fuel does not burn evenly and completely in the combustion chamber. Detonation is also referred to as pre-ignition, "engine knocks" or "engine pinging". Detonation can be caused by a variety of conditions including excessive ignition timing advance, excessive carbon build up in the combustion chamber, incorrect spark plug heat range and/or gap or using gasoline with too low of an octane rating.
To maximize the efficiency of the engine, a knock sensor is used to send a signal to the PCM. If a knock is detected, the PCM responds by adjusting the ignition timing until the "knock" stops. The sensor works by generating a signal produced by the frequency of the knock as recorded by the piezoelectric ceramic disc inside the KS. The disc absorbs the shock waves from the knocks and exerts a pressure on the metal diaphragm inside the KS. This compresses the crystals inside the disc and the disc generates a voltage signal proportional to the frequency of the knocks ranging from zero to 1 volt.
See Figure 1
Although the sensor is designed to detect internal engine knocks, a loose bracket or fastener near the sensor location could cause the sensor to mistake a loose bracket or fastener for an internal knock. A sensor that has come loose or has been replaced but over-tightened during installation, could also cause an incorrect signal to be sent to the ECM/PCM.
There is real no test for this sensor, the sensor produces it's own signal based on information gathered while the engine is running. The sensors also are mounted on the side of the engine block near the cylinder head. The sensors can be monitored with an appropriate scan tool using a data display or other data stream information. Follow the instructions included with the scan tool for information on accessing the data. The only test available is to test the continuity of the harness from the PCM to the sensor and make sure all of the electrical connectors are clean and secure.
REMOVAL & INSTALLATION
- Disconnect the negative battery cable.
- Locate the sensor installed in the side of the engine block. If the vehicle needs to be raised, raise and securely support the vehicle in a safe manner.
- Unplug the sensor connector.
- Using the proper size socket, loosen and remove the knock sensor.
- Carefully thread the sensor into the engine block.
- Tighten the sensor to 23 ft. lbs. (31 Nm).
- Attach the sensor connector.
- Lower the vehicle if raised for accessibility.
- Connect the negative battery cable.