Q: Knock sensor

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A knock sensor was put on this car 2 years ago. My sister took it to emissions and it didn't pass. The car was put on the machine and it is saying the car failed because of the knock sensor. Why is that, when it was changed 2 years ago
My car has an automatic transmission.

Hi There, The knock sensor is a component that creates an internal voltage signal based upon vibrations it detects as a result of detonation internally in the motor which creates a knocking vibration. An engine can ping (or knock) due to an improper combustion process. A "spark knock" is the result of combustion occurring too early. Early combustion can occur from carbon buildup inside the combustion chamber, a lean air/fuel mixture, and advanced ignition timing (spark plug firing too soon). This may be caused for many different reasons and will generally result in a check engine light which will store a specific engine diagnostic code in the computer. This will be helpful in determining what specifically may be causing the knock sensor to pick up these vibrations. I would suggest having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

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