The Symptoms of a Bad Knock Sensor

Your vehicle's engine is controlled by various sensors responsible for regulating important functions, such as fuel management, emissions, ignition timing and transmission shifting. One sensor in particular, called the knock sensor, acts as a sophisticated listening device in the engine. It detects any engine noises caused by detonation -- when fuel explodes in an engine's cylinder-- and adjusts ignition timing accordingly. If the knock sensor malfunctions, detonation is not properly regulated and major engine damage can occur. Recognizing the symptoms of a bad knock sensor and replacing it, may help you avoid costly repairs.

Check Engine Light

Usually a bad knock sensor will trigger the "check engine" light to flash on your vehicle's dashboard. Sometimes, using cheap gasoline causes detonation and triggers the power train module -- the engine's main control board -- to wrongly diagnose the knock sensor and send a false malfunction message via a check engine light. Try filling your vehicle with a higher grade of gasoline, and if the light is still flashing, consult with a mechanic.


If the knock sensor is not working properly, you will likely hear sounds emitting from the engine. You may hear loud thumping noises that become louder over time. The noise is a result of fuel and air igniting inside the cylinder, instead of reaching the point of combustion.

Other Symptoms

There are several other symptoms indicative of a knock sensor problem. The vehicle will often shake or vibrate and misfire when the engine is started. The engine may emit strong exhaust and burning smells due to the detonation in the cylinders. Fuel economy is often affected, causing the vehicle to burn more gas than usual and requiring frequent fuel replenishment. Also, your vehicle may display acceleration problems, such as dragging, hesitation or jerking from the engine during speed increases.

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