Knock Sensor — How to diagnose How does a knock sensor work? A knock sensor has a piezoelectric crystal inside that converts vibrations into an AC voltage. The greater the vibration, the higher the AC voltage and frequency. It’s used in engines to detect detonation (knock). The knock sensor can’t discriminate between vibrations from cylinder detonation or vibrations caused by hitting a pothole or rumble strip. So the car’s ECM also monitors the crank sensor. During detonation, there’s a noticeable drop in that cylinder’s contribution to engine rotation. If there’s … Read More
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