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What are knock sensor functions and symptoms?

May 24, 2016 | Engine Info

The Function

The main function of a vehicle’s knock sensor is to sense for vibrations that are caused by the detonation or knock of the engine. You will find the knock sensor on the intake manifold, the cylinder head or the engine block. Once there are vibrations sensed, the powertrain control module receives a voltage signal and uses it to change the timing of the ignition and stop it from detonating. By doing this, the engine will be protected from being damaged during pre-ignition. Remember that denotation in an engine is basically when fuel explodes in its cylinder and alters the timing of the ignition. So if the knock sensor fails then this detonation cannot be regulated and will result in huge damage to your engine. That is why it is important to recognize what the symptoms are of a failing knock sensor. Then you can replace it and avoid paying thousands of dollars fixing a damaged engine.

The Symptoms

When a knock sensor goes bad, the symptoms will usually be noticeable when you’re going at high speeds like on the interstate. The acceleration and fuel mileage will start to decrease for one thing. Also, your car’s computer system should notify you when there is a problem with the knock sensor. Either that or you’ll see the “check engine” light flashing on your dashboard. In rare circumstances, cheap or dirty gasoline will improperly cause the powertrain control module to falsely warn you that you have engine problems when you really don’t. So if you really want to be safe about this then you can use super unleaded gasoline instead of regular unleaded.

Aside from warning lights, you can also listen for noises that indicate a failing knock sensor. These will be thumping sounds that will come directly from the engine. As the knock sensor gets worse, the thumping sounds will gradually get louder and louder. This noise occurs because the air and fuel ignite in the cylinder rather than getting to the combustion point. Other symptoms include an engine misfire when trying to start the engine or even vibrating and shaking too. You may even see strong exhaust fumes emitting from the engine which gives off a burning smell in the car. Again, this is from the denotation of air and fuel in the cylinder. The worse symptoms will involve the car jerking, hesitating or dragging while in motion. Don’t let it get to this point. Listen for the early warning sounds and then take your car to an auto repair shop to get new knock sensors.

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