A Z71 version of the 2016 Chevrolet Colorado Diesel which won a 31 mpg EPA highway rating.

Not so fast. When General Motors asked the Environmental Protection Agency to issue its official fuel economy rating on the new Chevrolet Colorado Duramax diesel pickup, the agency took a little longer than expected, EPA officials asking if they could keep the test truck a bit longer than normal, says Mark Reuss, GM’s global product development chief.

The EPA is taking a much more careful approach when it comes to testing for emissions and fuel economy, Reuss and other industry officials tell TheDetroitBureau.com. And U.S. regulators are not alone. Germany’s Federal Motor Transport Authority says it will run new tests on dozens of vehicles sold in that country to ensure they comply with diesel emissions standards.

Those moves come in the wake of revelations – first announced by the U.S. EPA on September 18th – that Volkswagen AG had cheated on emissions testing for vehicles equipped with the maker’s 2.0-liter EA 189 diesel engine. A total of 482,000 of those vehicles were sold in the U.S., 11 million worldwide. Since then, VW has admitted to other emissions “irregularities.”

The VW scandal is “not a good reflection on the industry,” Reuss says, quickly adding that GM has not broken the rules with its own diesel products.

(EPA gives Chevrolet Colorado Duramax diesel 31 mpg Highway rating. Click Here for more.)

There has seen a small but steady expansion in the number of diesel-powered vehicles offered in the U.S. market in recent years, though the bulk of them are sold through European brands – so-called “oil burners” accounting for 25% of the total sales for Volkswagen of America.

VW has been accused of rigging the emissions testing of its Porsche Cayenne diesel.

But domestic brands are slowly expanding their own diesel offerings, Fiat Chrysler adding an EcoDiesel version of its Ram pickup, GM introducing new diesel variants of the Chevy Colorado and GMC Canyon trucks and the Chevrolet Cruze sedan.

The EPA is expected to take a much closer look to ensure that manufacturers aren’t hiding technology intended to let them game the system. VW used a so-called “defeat device,” special software design to detect when one of its diesels was undergoing testing to temporarily reduce emissions of smog-causing oxides of nitrogen.

The U.S. agency has already accused VW of cheating on additional models, up-market vehicles using a 3.0-liter diesel sold by the Volkswagen, Audi and Porsche brands. While the German maker insists it did not violate regulations with a system it claims actually improves emissions system performance at low temperatures. A final analysis is underway by the EPA.

But VW officials did admit last week that an internal investigation has uncovered “irregularities” involving at least 800,000 more vehicles. Engineers have conceded they took a variety of shortcuts in order to meet the aggressive emissions mandates set by recently ousted Volkswagen AG CEO Martin Winterkorn.

(VW giving $1,000 in gift cards, vouchers, to its diesel owners. Click Here for the latest.)

In recent weeks, European media have been abuzz with reports that other automakers have also cheated on emissions tests, both for NOx and carbon dioxide, the European Union implementing the world’s toughest CO2 mandates.

So far, no manufacturer but VW has actually been shown to be in violation though, as TheDetroitBureau.com recently reported, European diesel products almost all exceed test emissions levels substantially in real-world use – something not technically a violation of the law.

But the German transport agency, the Kraftfahrt-Bundseamt, or KBA, wants to take a much closer look. It is running new and more thorough tests on 50 diesel models from 23 different German and foreign automotive brands.

“Since the end of September KBA has been investigating whether further manipulation of emissions, of nitrogen oxides in particular, is taking place in the market,” the agency said in a statement.

While the KBA wouldn’t disclose the specific vehicles under review, it said the list of brands includes BMW, Chevrolet, Fiat, Ford, Honda, Jeep, Land Rover, Mercedes-Benz, Porsche, Renault, Toyota and Volvo, as well as Volkswagen.

So far, two-thirds of the tests have been run and an initial review of raw data indicates elevated levels of NOx “in some cases,” according to the agency. Whether that will hold up under more complete analysis is uncertain, and a violation does not automatically mean a manufacturer was knowingly cheating.

Officials in both Washington and Europe have indicated that they will be taking steps to ensure that they can detect hidden steps meant to fool conventional testing procedures. In VW’s case, the 2.0-liter EA-189 engine was programmed to detect when a vehicle was being operated on a dynamometer. Among other things, that meant there was no steering input and the vehicles were running in a carefully controlled room with set temperature and barometric pressure.

Going forward, some regulators have suggested they want to find a way to test for emissions under real-world conditions, something that could prove far more challenging, experts warn.

Emissions aren’t the only things regulators are looking closely at. Several automakers, including Hyundai, Kia and Ford, have been fined in recent years for misstating their fuel economy numbers — which are generally developed by the makers using their own labs and EPA testing procedures. Going forward, industry officials say, self-certification may be barred, with either the EPA or third-party labs taking over testing duties.

(More VW execs head for the exits as emissions cheating scandal grows. Click Here for the latest.)

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