The knock sensor senses a knock in the engine and indicates the need for less spark advance. When the knock sensor fails, the the engine will knock and could cause major damage to the engine. When it fails, a knock sensor replacement is necessary immediately to prevent damage to the engine.
When replacing a knock sensor, the technician may have to remove part of the intake manifold to reach the sensor. The electrical connector and the fastener holding the sensor is removed. Then the technician removes the defective sensor and cleans the area where the sensor was located. The new knock sensor is installed and torqued to the factory recommendations. Then the electrical connecter is installed and any PCM codes are cleared. Finally, a Drive Cycle Test Drive is performed.
A knock sensor replacement is usually covered under the federal emission warranty. Some manufacturers will cover the knock sensor under their factory warranty if the time and mileage limits are longer than those of the emission warranty. There are also extended car warranties available that will cover the cost of replacing the knock sensor under certain levels of coverage.