Sorry I don't have pictures of my actual repairs, but hope this might help somebody else.

I noticed one of the parking sensors was pushed into the bumper. After trying to get access from the trunk and under the car, I realized there was no easy way to get to it from behind. Removing the bumper looks like a huge job :

So my hack was as follows :
1) I used a nerf gun bullet with suction cup

2) While I could grab the sensor with the suction cup, I couldn't manage to get it to re-seat and the dart would detach.
3) While fiddling and failing for some time, i realized that there was a rubber gasket around the sensor, that looks like this :

4) Using a bent safety pin, I managed to pull off this gasket, and remove it. Note that it is thin, so be careful not to tear.
5) To get a better grip on the parking sensor, I used a hot glue gun to attach the dart more firmly to the sensor. This is easily peeled off later so don't panic!
6) With the gasket outside of the car, i cleaned it, and kept it moist with water. working over the nerf dart, i put the gasket into place in the bumper.
7) working slowly, i used the dart to pull the sensor back into the gasket from inside the bumper. The moisture helped to get it in without dislodging the gasket.
8) Working with my finger i carefully peeled off the dart, and removed the remaining glue from the sensor.

I can't imagine how much paying a dealer to remove the bumper (and probably telling me i needed a new sensor) would have cost, but my repair cost 2 nerf darts, and a bent safety pin.
I let my younger son help, and encouraged him to use outside of the box thinking... we tried some of his ideas like using thread or thin wire to reposition the sensor before we figured out the gasket issue.
Again, I hope this helps someone fix this issue quicker than I did!

Sean

 

Outstanding! I love solutions like this! Good job, and thanks for sharing.

 

I've used metal tape for ducts (NOT 'duct' tape) for some similar problems. I've never had a nerf dart handy.

 

I thought I'd share my own experience with this problem. I am a new X150 owner, just got my 2007 XK a couple of weeks ago. Love it. However, while washing it I noticed that the left rear sensor was slightly pushed in. While it ran through my mind that I should check here first (I have found this site invaluable for fixing my sadly gone XK8, which this car replaces), I didn't follow through. Instead I tried just attaching some chewing gum to it--which didn't work as it wouldn't adhere, but it also pushed it in a bit further. Then I thought I'd try one of those magnetic retrieval devices that look like a small antenna with a round magnetic disc on the end. It was the perfect size for the sensor hole, but not only did it not attract the sensor, I managed to push it all the way in. Thus, the OP's solution was not going to work unless I could first reposition the sensor back in the hole. Realizing what I'd just done was pretty much a facepalm moment. I bought one of those telescoping grabbing claw devices, although I wasn't sure how I was going to position the sensor since I couldn't actually see it, only the harness to which it was presumably attached. Also there would be no room unless I could slip a noose loop over it or something. When the device came, I could grab the harness, but the sensor was not in sight.

Given the posted video of how much work is involved to take off the rear bumper, I laid down underneath to confirm that there was really no other access. Well, there is no easy access, but by pulling down the black plastic undertray beneath the bumper just a bit on the driver's side edge, I was able to reach up past it (it could be removed, but that would just stop it digging in to your arm, mine wasn't on super-tight so maybe that helped) and past some metal beam and into the bumper. I could feel the harness, sensor, and actually reach the hole the sensor goes into. It's actually a sort of keyway / receiving slot with prongs around the edge. After fumbling around with the harness and getting it near the keyway, I looked from the outside and could see I had it backwards, the painted part was facing in. Back under the car, working blind with one arm up inside the bumper but able to reach my other arm so my finger reached through the hole from the outside, I was able to push it back into place and flush with the bumper. Engaging reverse, the loud noise from the sensor thinking it was hitting something (and warning light) was now gone. I cannot tell you how much I was kicking myself for not trusting my first instinct to look on here, and how relieved I am to have fixed it. I would try the nerf / glue solution if it happened again and there was no access (this was driver's side in the U.S. rear, don't know if the others are reachable). Also I highly advise you not to push on these things while waxing or otherwise, as it could be a huge headache or costly fix.

Anyway, happy motoring and looking forward to joining the conversation on here with you all.

 

Last summer on my 07XK, my right rear outermost sensor got pushed while washing the car.
lucky it only got pushed in about an eighth of an inch.
Also lucky I was able to push it back into position with a long screw driver.
I am very careful washing the rear bumper now.
Seems odd to me that only a little friction holds it in place, should there not be something more positive to keep it in place?
I wonder how other brands keep sensors in place?
Bob

 

Mine was also loose and after reading your thread, I went to inspect. I thought, let me check first if I cant reach it from behind the bumber and viola, I just pushed it right back! Maybe not all of them are reachable. Great innovative job from you regardless. Hats off