CEL came on today on my 2004 A6 and I pulled P1850 Data-Bus Powertrain Missing Message from Engine Control. Searched on the fourms and also on the web, but nothing that gives any info on what the possible cause is, or a fix. Any advice is much appreciated. Only mods done thus far are 710N Dv's, Samco TBB, GIAC-X, exhaust, K&N panel and airbox mod.