Initially hampered by the lack of punch of its diesels, Mazda is now also having to engineer an after-treatment emissions system for the 6 sedan in order to comply with federal standards. Diesel exhaust fluid (DEF), commonly referred to as AdBlue in Europe, is a urea solution that lowers the NOx levels coming out the back. The downside is that you need to refill the reservoir at certain intervals, which not only adds to your servicing costs, but also takes up some of the trunk space.On many occasions, Mazda’s press statements said low compression and special cylinder head design eliminated the need for AdBlue, but it seems this isn’t the case.A recent report from the The Truth About Cars suggests the Mazda6 Diesel won’t be ready until the 2016 model year, coming out in the second half of next year. Its arrival could be timed to coincide with a mid-life facelift. The 6 faces stiffer competition than ever in a segment where fuel economy and extra features are the main selling points.