Using SD as external drive

I use this code for uEnv.txt, my SD is named ‘BBB_Ext’:

mmcdev=1 bootpart=1:2 mmcroot=/dev/BBB_Ext ro optargs=quiet

I use this line in my fstab file:

/dev/BBB_Ext    /media/card     auto     auto,rw,async,user,nofail  0  0

It boots with 3 LEDs and no connection to the computer. Without the SD card, it is detected and I can SSH properly.
Help greatly appreciated!