I am trying to use my Clip+ with the media-in interface on my VW Mk7 Golf. The car infotainment system reads Clip folder structure OK but does not recognise files in music folder. The files are .mp3 format and I have tried using in MSC and auto-connect USB mode when adding files to Clip. Yet to try MTP mode but will try next. Would appreciate any advice if anyone has got this working. BTW, when connected to media-in in auto-connect USB mode it immediately finds slot radio and plays the slot radio introduction jingle!
Auto Defect mode defaults to MTP mode so I doubt trying that is going to help. Did you transfer any of your files while in this mode? In MSC your stereo should see your player as any other ‘dumb’ flash drive. Personally, I would try formatting the player which will remove everything you have put on it. Change the USB mode to MSC and re-load some of your files and test it out.
Another possibility (although remote) . . . what is the bit-rate of the .mp3 files? Too low or too high may be causing the car’s stereo system some problems.
You could also try NOT putting them into the Music folder, but simply in the top (or root) directory so the path for your stereo to read is Artist\Album\Song rather than Music\Artist\Album\Song.
Edit: One more thought . . . have you tried searching and/or asking on a Volkswagen forum. I’m sure you’re not the only one with this car and sound system that wants to use an external mp3 player through it. Somebody who has already “been there, done that” would know for sure what works. 
My son has the same with his iPod Classic. We tried with the SanDisk mp3 and manual set USB on MTP and it works. The car is a VW Golf 2013. So you are on a good track.
Some car stereos only see mp3 files that are in the root of the player. Are you sure your mp3 files are at a supported bitrate? Are you sure they are mp3 files and not WMA? For example some car stereos don’t support VBR, and only support constant bitrate files. Some might not support higher bitrates, or only support certain specific bitrates. it might even be the case that the car stereo doesn’t put out enough power for the Clip+.
Imo this seems like too much trouble. I suggest that you get a cheap usb drive and use that in your car.
Replying to Tapeworm, Otto, and JK98 - thanks for the responses.
I tried everything Tapeworm suggested (that includes what you said JK98) but it still failed to work normally. It would play about 10 secs of the first track (like a scan was requested) and then stopped and lost connection. It didn’t make any difference if in the root folder or a sub-folder. I created new files at a specified within spec bit rate and even obtained another (new supplier) interface cable in case of some sort of cable issue. I can only think it must be down to the version of the Sansa firmware.
Anyway, I’ve subsequently obtained a USB interface cable for around £11 and a normal stick works like a dream. It’s better than the Sansa Clip as there is no need to worry about turning on/off, disconnecting if its use is required elsewhere, etc.
Thanks for your feedback and suggestions on this, much appreciated. 
