Get thee to a dealer. I had one go, they just replace it. It is an expensive part, but I assume you are still under warranty.
'05 E90 325i 6sp Man SG 118,032km on the odo (retired) | '06 E90 325i Step SG 121,021km on the odo (retired)
'08 E90 325i LCI Step SG 130,024km on the odo (retired) | '13 F30 328i M-Sport Step 49,709km on the odd (retired)
'14 F10 535d M-Sport Step 50,179 on the odo