What is a Vehicle Knock Sensor and What Does It Do?

What is a Vehicle Knock Sensor and What Does It Do?

The knock sensor is a piezoelectric sensor that consists of a sensing crystal and a resistor located on the engine block, cylinder head or intake manifold.

Its main function is to detect the noise vibrations caused by engine knock or detonation. This sends a signal to the Powertrain Control Module (PCM) to alter the ignition timing and prevent detonation.

This happens due to the information being compared with the preset tables to identify a valid knock or ping, protecting the engine from a damaging knocking or pre-ignition.

Why it’s So Important?

Keep in mind that detonation in an engine happens when fuel literally explodes in its cylinder and alters the time of the ignition. A faulty knock sensor can lead to the detonation not being regulated, which results in excessive damage to the car’s engine.

Recognizing what the early symptoms of a failing knock sensor look like is crucial in order to avoid fixing a damaged engine later on, which can cost thousands of dollars.

Symptoms of A Faulty Knock Sensorknock sensor

The symptoms of a faulty knock sensor are evident when going at high speeds like driving on a highway:

  • The acceleration and fuel mileage will start to decrease for no apparent reason
  • Car’s computer system should notify you there is a problem with the knock sensor
  • The “check engine” light will flash on your dashboard
  • Cheap or dirty gasoline will improperly cause the powertrain control module to falsely warn you that you have engine problems when that’s not true

When the problem starts to escalate you’ll notice symptoms like:

  • Noises like thumping sounds that come directly from the engine will be heard. This occurs due to the air and fuel igniting in the cylinder, rather than getting to the combustion point.
  • Engine misfires, shakes or vibrates when trying to switch-on
  • Heavy exhaust fumes with a burning smell will come from the engine. This is a result of unregulated air and fuel denotation in the cylinder
  • Car jerking, hesitating or dragging while in motion

Knock Sense Maintenance

There are some car models famously known and having a bad reputation for knock sensor failure. Price comes to the table when talking about maintenance, as cost of replacement normally fluctuates between $140 and $448.

On the same token, the total estimate of labor cost varies from $52 to $333, while separate installation parts costs between $88 and $115 before taxes and fees.

Normally engine light and knock sensor related OBD codes will tell you something’s wrong and you should go to a technician right away.

The OBD codes that indicate a faulty knock sensor are:

  • P0324: Knock Control System Error
  • P0325: Knock Sensor 1 Circuit
  • P0326: Knock Sensor 1 Circuit Range/Performance

However, keep in mind that some cars are not able to detect that, hence the problem becoming more difficult to diagnose. If you start to notice any of the symptoms already mentioned, ask your mechanic for a knock sensor inspection.

To begin, the technician conducts a visual inspection of the sensor and associated wiring by scanning the system for any issues.

If the knock sensor wiring harness and electrical connectors are performing correctly, then the knock sensor will be tested.

Most cars normally have one electrical connector per knock sensor, and there may be another knock sensor on the engine. In those cases, the oil must be drained to change both the knock sensor and the oil filter.

If something suspicious gets detected, removal might be necessary for further bench testing.

The diagnosis usually gets confirmed right away after testing so that any failed component can be replaced.

The vehicle will be tested to ensure the problem doesn’t strike back.


What’s Next

If you are thinking about saving money, and rather do the knock sensor replacement by yourself, replacement can be made at home, because only a few basic tools are needed.

Nevertheless, take into account that proper diagnostics is vital to hit the nail on the head, as there might be many other components besides the sensor that might cause the knocking. In which case it might have to do with further engine damage rather than a faulty knock sensor.

In those cases, the best idea is to contact a professional. Their ability and the tools they have for properly troubleshooting this kind of problem makes it way more reliable than trying to self-diagnose the issue at home. If your car keeps having engine problems and you’re not sure about the cause of these visit our website and we’ll provide you with the best car information so you can make a decision.


Bryce Newell is an automotive enthusiast who loves to write about the latest news, products, and DIY projects. While Bryce is an amateur in the field, he is passionate about cars and has been since he spent weekends in the garage helping his dad rebuild a 68 Dodge Charger as a kid.

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