PSA Peugeot Citroën has become the first carmaker to admit that its published fuel-economy ratings simply do not match up with reality.

The announcement comes in the wake of increased global scrutiny of automakers' fuel-economy testing procedures in response to the Volkswagen diesel emissions scandal.

PSA conducted real-world fuel-economy tests to bolster consumer confidence in the wake of the VW scandal.

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But the investigation found that 28 Peugeot, Citroën, and DS models returned far lower fuel economy in real-world driving than they did during laboratory testing.

The 14 Peugeot models tested averaged 44 percent higher fuel consumption, 11 Citroën models averaged 39 percent higher consumption, and three DS models showed 40 percent higher fuel consumption, compared to official New European Driving Cycle (NEDC) ratings.

The test group including multiple versions of some models to encompass the different powertrains available in those models.

Portable Emissions Measurement Systems (PEMS) on a Peugeot 308

Portable Emissions Measurement Systems (PEMS) on a Peugeot 308

Measurements were taken on public roads, with passengers and luggage onboard and climate-control systems in use, according to a PSA press release.

Testers used routes that included 25 kilometers (15.5 miles) of "urban" driving, 39 km (24.2 mi) of "rural" driving, and 31 km (19.2) of "motorway" driving.

Fuel economy was measured with Portable Emissions Measurement Systems (PEMS), the industry standard for on-road fuel efficiency testing and the same type of equipment used to uncover Volkswagen's "defeat device" software.

ALSO SEE: Why European Gas-Mileage Ratings Are So High--And Often Wrong (May 2014)

The tests were conducted in concert with advocacy groups Transport & Environment (T&E) and France Nature Environment (FNE), and audited by Bureau Veritas.

The PSA fuel-economy results were in line with the rest of the industry, Greg Archer—who worked on the test program for T&E—told Bloomberg.

The gap between window-sticker fuel economy and real-world results is an "open secret," Jean Thevenon, transport and sustainable development leader for FNE, told the news service.

Portable Emissions Measurement Systems (PEMS) on a Peugeot 308

Portable Emissions Measurement Systems (PEMS) on a Peugeot 308

In April, PSA offices in France were raided by government investigators as part of an emissions-testing probe.

At the time, PSA said that all of its cars complied with European emissions standards.

Even before news of the Volkswagen diesel scandal broke, many analysts had questioned the efficacy of Europe's NEDC testing cycle.

MORE: EU Commission Accepts 'Flawed' Emission Rules For On-Road Testing

NEDC is known to be much more optimistic than the U.S. EPA testing cycle.

While it also relies on laboratory rather than real-world tests, the EPA regularly adds "adjustment factors" to bring its published fuel-economy ratings closer to reality.

This can be most clearly seen in the 54.5 mpg Corporate Average Fuel Economy (CAFE) target carmakers must meet by 2025, which translates to only about 38 or 39 mpg on the window sticker.


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