Daimler Suspected of Using Diesel Defeat Device

Some Mercedes-Benz diesel models are equipped with software that may have helped them pass emissions tests, according to a report published by German newspaper Bild am Sonntag.

The report, citing information Bild Am Sonntag says is contained in a U.S. Department of Justice investigation, reveals engineers from Mercedes-Benz parent company Daimler developed several software programs that allowed unspecified diesel models to pass U.S. emissions tests through manipulation of the engine and its selective catalytic reduction system.

The software programs are alleged to have been tailored to the specific demands of various cycles in the U.S. emissions-testing procedure, allowing the Mercedes-Benz diesels to run in an ultra-clean state but only for limited periods of time, after which the engines were switched into a so-called “dirty mode.”

Mercedes-Benz is not commenting on the allegations of diesel-emissions manipulation.

The manipulation software programs allegedly used by Mercedes-Benz to allow its diesel models to pass the U.S. tests are similar to those developed by Volkswagen and threaten to drag it further into the Dieselgate scandal.

According to the information cited by Bild am Sonntag, one software program developed by Daimler is the “Bit 13” function. It commands the diesel engine switch to “dirty mode” once it emits 16 grams of nitrogen oxide. This corresponds to the duration of the U.S. highway test cycle, the newspaper says.

Also suspected of being used is the “Bit 14” software function. It switches the engine into so-called “dirty mode” under certain temperatures and preset periods of time. This function allegedly is particularly suited to allowing cars to pass the FTP-75 warm test cycle.

Another software function called “Bit 15” is claimed to have been used during the US06 test cycle. It is programmed to switch off the SCR exhaust-gas after-treatment system after 16 miles (26 km).

In addition, Bild am Sonntag says U.S. investigators have uncovered a further suspicious software function within the control system of various Mercedes-Benz models. Called Slipguard, it detects when the car is being tested on a rolling road and is claimed to influence the release of urea-based AdBlue solution into the SCR system.

The report on Mercedes-Benz’s alleged diesel emissions manipulation follows news that the German Ministry of Transport is set to demand the German automaker issue a recall for diesel versions of its Vito commercial van due to discrepancies.

According to sources, tests carried out on the Vito reveal its SCR filter are programmed to reduce the injection of AdBlue to allow it to be filled during service intervals – thus reducing its efficiency and leading to higher NOx values than those claimed by Mercedes-Benz.