I just got that notice and have an issue with excessive black smoke when the vehicle is going uphill under load, the unit has 160,000 kms on it and I was wondering if the emission parts are still at that mileage under a warranty. I did not buy this unit new and have no operators manual with it.
Your Mass Air Flow sensor may be dirty and giving a bad reading. A $13 dollar can of MAF cleaner might fix this - takes about 1/3 of a can to do the job.
If it is not a dirty MAF, you might need injector service. I clean mine about every 80,000 km.
FWIW, any dealer can look up your VIN and see if you are still under emission control warranty. With all the diesel scandals going down I would bet the companies are happy to take care of problems.
Finally, diesel particulate matter, AKA smoke, is very toxic and carcinogenic. I used to work in air pollution control and controlling diesel pollution was a big focus area. You will be doing the lord's work if you take care of this - poisoning drivers behind you ain't right!!