Emissions fail

My 2007 Mercedes-benz E320 W211 CDI estate (not BLUEEFFICIENCY) has failed its MOT on emissions. It would seem the emissions test limit has been reduced from 3.0 to 0.90 l/min. The car’s mean absorption coefficient tested at 2.65. Later it did pass, but I don’t know the results. Do you have any thoughts on this? I am worried about next year’s test. Gareth Owen

The emission level for your Mercedes is 1.5 m-1 and the gov. uk site states that the minimum level should be 3.0 m-1 or the plate value, whichever is lower. Although the MOT has changed with regard to diesel emissions, this was in the form of visible smoke.

I can see from the MOT history that your vehicle has covered 106,000 miles and that you normally cover around 7000 miles a year, but this doesn’t indicate if you usually do short or longer runs. I would generally recommend the vehicle is given a good run before being presented for its MOT. This helps to ensure the emissions are at the optimum level. If possible, it is a good idea to ensure the engine is fully warmed up.

As you mention that the car did later pass the MOT, you haven’t given any details of remedial work. I suspect the vehicle was given a run before the second exhaust readings were taken. If this is the case, I do not believe you need to worry about future tests, provided the vehicle is given a good run first and is at running temperature.