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Daimler introduced BlueTEC in the Mercedes E-Class (using the DeNOx system) and GL-Class (using SCR) at the 2006 North American International Auto Show.  At that time, these BlueTEC vehicles were 45- and 50-state legal, respectively, in the United States (a 45-state vehicle does not meet the more stringent California emission standards that have also been adopted by four other states). 

By 2010 a BlueTEC version of the Mercedes Sprinter was released.  The BlueTEC systems allowed the elimination of much of the EGR in that vehicle's engine, which as a result gives 188 horsepower (140 kilowatts) compared to the non-BlueTec engine's 154 horsepower (115 kilowatts).[12]

The BlueTEC system was created because the properties of the Diesel cycle that give diesel engines higher fuel efficiency also lead to relatively higher emissions of certain pollutants compared to Otto cycle engines.  High compression ratios and lean air-fuel mixtures make high combustion temperatures, which results in more nitrogen oxides being produced during the combustion.  While the particulate matter can be controlled with higher injection pressures and particulate filters, the big challenge is limiting NOx; Tier 2 regulations in the US are 0.07 grams per mile of NOx, which is ⅛ of the 0.40 limit in the European Union.[14][citation needed]

A DeNOx catalytic converter begins a preliminary removal of oxides of nitrogen. 

A particulate filter traps and stores soot particles, burning them off when the filter gets full. 

If the above are not sufficient to meet the prevailing emissions regulations, a Selective Catalytic Reduction (SCR) catalytic converter will convert the remaining nitrogen oxides to nitrogen and water; so-called diesel exhaust fluid (solution of urea and water) is injected into the exhaust gas stream to enable the conversion.  In order to prevent vehicles from breaking emissions regulations, the engine may go into a limp-home-mode if the DEF tank is depleted; drivers are instructed to keep the tank refilled as necessary.  Some commercial vehicles are equipped with a request or inhibit switch which allows the DEF injection to be "postponed" as it can reduce power output and increase temperatures temporarily; if the vehicle is climbing a grade, for example, it may be necessary to delay the cycle. 

The Netherlands' official automobile inspector TNO, on behalf of the Dutch Minister of the Environment, conducted an on-road tests of a C-Class Mercedes C220 CDi BlueTec diesel and determined it emitted more than 40 times the amount of cancer-causing NOx than in the lab test.[15] The tests were done at temperatures below 10 degrees Celsius (50 °F).  Mercedes says it is permissible for the BlueTec engine to emit 40 times more NOx when the temperature is less than 10 °C (50 °F).[16]

As of 2016 April 22, Mercedes-Benz USA disclosed it is under investigation by the Department of Justice for potential discrepancies over its diesel emissions certifications, according to a Daimler statement.  The DOJ effectively told MBUSA to begin an internal investigation "to review its certification and admissions process related to exhaust emissions in the United States," Daimler said.  The company "has agreed to cooperate fully with the DOJ."[17]

In Feb 2018, German newspaper Bild am Sonntag reported that US authorities investigating Mercedes have discovered that its vehicles are equipped with illegal software to help them pass United States' stringent emission tests.  The claimed defeat devices include a "Bit 15" mode to switch off emissions after 16 miles of driving (the length of an official U.S. emissions test), and "Slipguard" which tries to directly determine if the car is being tested based on speed and acceleration profiles.  Bild am Sonntag said it found emails from Daimler engineers questioning whether those functions were legal.[18][19][20]