I recently bought a 2011 335is and one big thing that has been bothering me is that the drivers side seatbelt handover hasn't been working. My local dealer told me this is not covered under the CPO warranty... so yeah. After some exhaustive researching, it seem there are two possible causes for this.
I have spent quite some time researching this issue and diagnosing it on my own car and as far as I can tell, there really isn't an exhaustive post on this. There are people complaining about it for sure. However, responses to the complaints seem to be almost exclusively in one of two camps... both have people who say the reported fix has worked for them, but they are very different issues. Here they are:
1. The seatbelt itself is worn in a manner that the handover cannot hold it properly.
2. The handover arm itself is broken.
For my car, it's been pretty easy to diagnose which issue above is actually causing the failure, so I wanted to create a post that would help others looking for consolidated information and help figuring out their own issues.
1. This should be pretty easy to diagnose. Look carefully at the seatbelt. The assumed issue is that the seatbelt is so flexible that the arm grabs it, but bends the belt itself so much that it can't hold on. If you can see any bumps, waves, etc with the seatbelt on the problematic side this is probably the issue. A kink along the edge the extender/handover arm hits. A fold/crease along the middle. Things like that. If there are no visible issues with the belt itself, you can also attempt to diagnose this issue by pulling 6"-12" of belt out of the b-pillar and holding it down at the floor in the backseat where the bottom of the belt attaches anyway. Then open/close the door and see if some "undamaged" seatbelt gets successfully grabbed by the arm.
The recommended fix (by online people anyway) is to iron/starch the seatbelt where the arm hits it. Possibly even iron a crease in it that is opposite the one that you find. The point is to make the seatbelt more rigid in the area where the arm hits it.
Here is a link to a post about this issue:
http://www.e90post.com/forums/showthread.php?t=588596
2. This is a mechanical failure of the arm itself. IMO the easiest way to detect this issue is to compare both sides and see if there is a difference in how the arm itself acts when attempting to grab the seatbelt. My car had this issue and it was pretty clear when comparing the broken drivers side with the working passenger side. The drivers side arm did not snap out (towards the belt/center of the car, not forward towards the seat) nearly as fast or as strongly as the passenger side. Another thing I noticed is that the hook itself seemed like it didn't want to stay properly extended when I tried to push it in compared to the passenger (working) side. I think this is a little bit harder to diagnose directly, but if you can rule out #1, it seems like a very good chance it's this.
The cause of this issue seems to be that some of the internals of the arm are actually broken. Honestly, I'm not entirely sure how the arm itself is supposed to work, but I can say that the post/video fix linked worked for me:
http://www.e90post.com/forums/showpo...7&postcount=24
(note that this video seems to have the exact same images as the e90 post link, though I don't know how they are related, if at all)
The post is helpful because it explains the issue, but the video gives more detail about the pictures. Some notes about the process. First of all, to remove the arm so that you can examine it, you simply need to close the door so that the arm extends and then grab the end of it and pull. It will take a bit of force, but the last 8" or so will pull out. Just grab the end of the arm and give it a tug. Once you are done working on it, open the door again so the rest of the arm extends out and then push the part you pulled out back into the rest of the arm.
As for actually fixing things. I recommend both reading the above post and reviewing the video.
I didn't find it necessary to actually drill a hole and put a screw in the arm. Simply removing the broken part and the spring was sufficient for me.
The pics provided in the above post and video are kind of hard to understand, but once you pull things apart it seems pretty clear. Just in case, I am attaching a couple of those pics with comments added via MS paint. Credit for the pictures themselves to the guy who originally posted these images (linked above) I simply used MSPaint to add some comments.
Be careful when removing the broken part and the spring!! When I did this on my car, the spring and metal bit shot out of the arm and actually hit my glasses. I hate to think what would have happened if I wasn't wearing them!