I'm 4 years late to the party, but in trying to locate my knock sensor I ran across this forum post. I just replaced mine and thought I'd share my experience with the interwebs.
I also own a 2003 Hyundai XG350L. The sensor is located under the intake manifold, which is a terrible location. You have to first remove the intake plenum (first picture), disconnecting any wiring, tubing, and air intake while keeping track of where they reconnect.
Second, you have to remove the intake manifold (second picture), which also entails removing your fuel injectors. The hardest part about removing the intake manifold is removing a bolt on the end near the timing belt that can only be accessed from underneath the timing belt cover. With some finesse I was able to get it out and, harder still, put it back in. I circled the knock sensor in the picture. Normally it would have a wire coming out of it, hence the reason I was replacing mine.
You might as well replace the plenum gasket and intake manifold gaskets while you're at it. Also, try to keep stuff from falling into your engine, unless said debris is magical make-my-engine better juice. In which case let me know where I can find that.
Monday, June 8th, 2015 AT 5:55 AM