As Mercedes continues to fight to recover from a diesel emissions scandal, the company’s diesel truck, the Mercedes-Benz E-Class, continues to suffer from problems.

In a new survey, a group of academics from the University of Warwick and the University at Buffalo found that Mercedes had installed more than 200 of the trucks’ diesel engines without an environmental assessment, and only 24 had been tested for emissions.

A third of the cars’ engines were still faulty, the study found, while the remaining 23% had been replaced.

“In many cases, the vehicles were being used for extended trips,” said Dr. Richard Schulte, an expert on environmental health at Warwick.

“It’s very difficult to know what the actual safety of these vehicles is.

The question is, why did they not test these vehicles?”

In the study, published in the Journal of Transportation Planning and Analysis, Dr. Schulten and Dr. Stephen C. S. Anderson, a Warwick doctoral student, asked about 3,200 drivers, truck drivers and passengers what vehicles they used on the road and at home and whether the vehicles had ever been inspected by the EPA, which is responsible for testing and certifying diesel-powered vehicles.

Of the 2,600 respondents, 1,700 said they had used the trucks or SUVs on the roads, with another 1,000 saying they used them on their own property.

“We found that the most common reason people had for not being tested was because they did not have a valid driver’s license,” Dr. Anderson said.

“If someone is under 18 and they don’t have a driver’s permit, they’re not eligible to drive the vehicle.”

When asked if the vehicles should be tested, more than a third of respondents said they should not, while a quarter said they would consider not driving the vehicle.

The study found that many of the diesel trucks were not tested at all.

Only a handful of diesel-engined vehicles, including the Mercedes, have been tested by the agency since 2012, and the EPA has not yet certified any of them.

But Mercedes has continued to push for more testing.

“The EPA has asked for more and more diesel-fueled vehicles,” said Mercedes-Daimler executive Vice President and General Manager of Diesel Vehicles Dr. Christian Neuer.

“And we will continue to push them.

We are not saying that we have no options, we are saying that it is not a priority.”

The company has said that the new Mercedes-Class diesel trucks will be certified in 2019, and that the EPA will begin testing in 2020.

The EPA has said it is testing the new vehicles to make sure they meet federal safety standards.

A spokesperson for the EPA did not respond to a request for comment.

The findings come as the EPA is weighing whether to take over the certification of the vehicles and expand its oversight of the fleet.

The company said the diesel truck is among more than 1,600 vehicles the agency currently oversees.