OK, so there i was writing a nice bug report to send to bugs@empeg, going through all the steps to demonstrate the problem when whadayaknow, it works!

I've figured it out, i can connect over serial no probs, with my normal user account. If i run emptool or upgclient as root then it won't connect. This makes no sense to me at all, becuase root should have full access to everything.

[dantheperson@danski empeg-car]$ ./emptool --serial /dev/tts/0
2000 Checking connection [Done] 2121 Downloading
[...snip...]

[root@danski empeg-car]# ./emptool --serial /dev/tts/0
4001 Failed to open device /dev/tts/0, errno:2