Hi All this is my first post though I have been and avid reader since I bought my MB around 18 months ago. I have searched through the posts looking for potential solutions but nothing is really jumping out at me. I have had my car, a 2012 W204 C200 CDI 7G Auto Estate for about 18 months. It has full MBSH throughout its 130k mile life so far. Over the time I have had it, I normally get around 50-55MPG on the drive to work and 55-60 on Motorway runs. Last year when the weather turned cold, the MPG dropped little, but it came back in the spring. Before Christmas, I had an engine warning light so I took the car within 1 day to MB to look at. It was a failed DPF sensor which they replaced and reset the codes. Since that day my MPG has dropped, with 45 or less to work and 50 on long runs. I have done around 3000 miles since. It has been back to MB for a check and they are showing no error codes. They replaced the air filter last week but I am still not seeing any improvement. Is there something I am missing? The thermostat is good and temp is steady where it should be. Tyres are inflated normally. I am using the same brand fuel as always. Of course I cant be sure that the DPF sensor change and the drop in MPG are related but it is coincidental. The weather was turning colder before Christmas BUT we have also had mild days without any improvement. Any suggestions as to where to look next? Is there a valve or sensor that needs cleaned that just doesn't show up on the computer diagnostics? And where is the inefficiency going, is there unburnt or poorly burnt diesel?