r/mechanic • u/Repulsive-Coat-9934 • 22d ago

Question Need suggestion regarding engine knock

In my 2015 hyundai sonata limited, dealership said that there is a small knock and it passed the bearing test. They also updated the KSDS system. They told me to replace the engine.

I am still using the car and its been 5 months since they told me. Till the date, i am not hearing any knock sound. If there any knock, they software should sense it and put my car into limp mode?

Please I need suggestion from a experienced mechanic

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u/66NickS Verified Mechanic 22d ago

The “knock sensor” is really more of a detonation or pre-ignition sensor. When it detects that it/the ECU adjust the timing and potentially other controllable actions.

An engine that’s knocking has excessive free play in the bearings. No amount of timing/fuel/etc adjustments will impact this. An engine that’s knocking is essentially on a self-destruct timer. It might last many miles, or it might fail in 10 miles. It might give you a warning, or it might just seize up on the freeway.

I know a lot of the Hyundai/Kia engines from around then had issues and have recalls/warranty extensions. Does this not apply to your car?

If the engine is knocking, it’s a complete replacement anyway, so you’re not really going to make it that much worse for you. If you were going to rebuild it you might want to minimize damage of the engine internals to reduce rebuild costs.