Knock Sensor

Knock Sensor

Unlike old-school carbureted engines, their fuel-injected counterparts run very smoothly and efficiently. In large measure, this happens thanks to an array of computer controlled sensors which monitor engine operation and conditions. One of them is a knock sensor.

Just like its name suggests, a knock sensor detects engine knocking and pinging caused by abnormal combustion inside the cylinders. It is mounted on the cylinder head for its maximum efficiency and ease of installation. If the sensor detects engine knocking, it sends signals to the engine control unit that changes ignition timing to avoid backfiring and misfiring. This allows for preventing damage to the engine and related components and prolongs their service life.

In some cases engine knocks can be caused by a low-quality gas, so it is recommended to check the quality of fuel before replacing the sensor. However, if the source of knocks is a faulty knock sensor, you may experience the following issues:

Engine knocking and pinging

Your engine control unit relies on the knock sensor to control ignition timing. If the sensor fails to operate, the control module won’t know when it needs to change the timing, resulting in knocking and pinging sounds coming from the engine.

Illuminated check engine light

A properly functioning knock sensor continually communicates with the engine control unit. If the computer does not receive any signals from the sensor, it will turn on the check engine light and store a specific trouble code that can be read with a special scanner.

Reduced performance 

Incorrect ignition timing due to improper knock sensor operation may cause the engine to run inefficiently. As a result, it will not be able to provide enough power and torque when you press on the gas pedal.

Increased fuel consumption

Overly retarded ignition timing will increase your vehicle’s fuel consumption since your engine needs more fuel to compensate incorrect timing.

Knock sensor troubleshooting and replacement

A knock sensor is not repairable, so it must be replaced with a new unit if it fails. However, before replacing the sensor, a thorough diagnosis is recommended to prevent unnecessary replacements and repairs. Your mechanic will need to use an oscilloscope or a similar tool to check its operation. He or she will simulate engine knocks to check the voltage output provided by the sensor. If it is in proper condition, it should fluctuate when knocking is present.