knock sensor?

[Euphman06]

Can anyone tell me what a knock sensor really does? I'm pretty sure it detects a knock in the engine and makes the engine run differently so it wont hurt the engine.. Mine seems to be not working and setting off the check engine light, however I never heard a knocking, and this happened twice now. You think its just a faulty sensor or something else. What would cause a knock in the engine?

[THAWA]

You're right about what it does. It doesn't only detect knock though, any abnormal sounds/vibrations can theoretically cause the sensor to send a signal to the ECU. It retards ignition timing. I would be willing to be it is a bad sensor. If it's the original, which is fairly likely, you should replace it ASAP. There is a TSB out about it with an upgraded sensor to replace it. The first ones were prone to cracking. As for what causes an engine to knock, there's a few different kinds of knock, so various things can cause it, though in the context, preignition and detonation are the ones the sensor is looking for.

[Euphman06]

Would you know how much it costs to get one repaired? I have a 95 legacy.

[THAWA]

if you do it yourself $50-75 dollars depending on where you get it.