BERLIN (Reuters) - German environmental lobby group DUH turned on carmaker Daimler on Wednesday, saying test results had shown nitrogen oxide emissions from one of its Mercedes diesel models far exceeded European legal limits.
Daimler (DAIGn.DE) described the results from a Mercedes C-Class 200 CDI as "questionable", saying the model used technology that met European Union standards and threatening legal action should "false claims" damage its reputation.
Citing tests carried out by the University of Applied Sciences in Bern, Switzerland, DUH told a news conference that the car, a 2011 model, had released emissions of nitrogen oxides (NOx) that were more than twice the legal limits when tested with a warm engine under new European testing cycles.
The carmaker took issue with DUH's assertions. "The test results are questionable as the conditions of the test are not clear. We don't know the specific car, the temperature at the time of the tests, the loading weight," a Daimler spokesman said.
Fellow German carmaker Volkswagen (VOWG_p.DE) is engulfed in a scandal after rigging the results of exhaust emissions tests in the United States.
DUH has made charges against a number of other motor manufacturers. In October it said a model built by General Motors' (GM.N) Opel division had shown excessive emissions of nitrous oxide, an assertion that was denied by Opel at the time.
French rival Renault (RENA.PA) has also contested findings cited by DUH that one of its minivans released toxic diesel emissions 25 times over legal limits.
Daimler said in a statement on Wednesday that the car tested in Switzerland used technology certified in 2007 that met the EU's Euro-5 standard. It acknowledged that results under real driving conditions often differed from those in a laboratory.
In September, DUH accused Daimler of also rigging emissions data, charges the company denied at the time.
It repeated the denial on Wednesday, saying: "We reserve at all times the right to take legal action should false claims or unjustified allegations damage the reputation of our company."
The discrepancies between laboratory-based results and real-world emissions measurements are part of a wider pattern that affects the entire auto industry and not just VW, Opel and Renault, according to DUH.
Axel Friedrich, a former official at the German environmental protection agency, said this was also the case with the Mercedes model. "If we had tested other vehicles from other manufacturers, we would have determined the same or similar results," he told the DUH news conference.
Friedrich is a co-founder of the Washington-based International Council on Clean Transportation (ICCT) which commissioned the original investigation that led to the exposure of VW's test-rigging in the United States.
Separate tests commissioned by German public broadcaster ZDF, also conducted by the Swiss university and aired on Tuesday, found that a BMW 3-Series 320d model released more toxic diesel emissions in real-world testing than in the lab.
BMW (BMWG.DE) denied its cars had the kind of "defeat device" that VW used to manipulate the tests.
"Our vehicles carry no illegal devices," a BMW spokesman said on Wednesday. "The emissions behavior does not distinguish between a vehicle on a dynamometer or in on-road use. We emphatically reject any speculation to the contrary."
Separately, public prosecutors in the German city of Stuttgart said on Wednesday they were investigating whether staff at auto parts supplier Robert Bosch GmbH were involved in the rigging of emissions tests by Volkswagen.
Stuttgart-based Bosch [ROBG.UL], which makes a diesel engine management program used by several top automakers including VW declined to comment on specific investigations.
A company spokesman said: "We are cooperating in principle with all authorities who want to contribute to the clarification of the facts."
Additional reporting by Ilona Wissenbach; writing by David Stamp; editing by Susan Thomas and David Clarke