Fraunhofer Study Finds Some PHEVs Use 3 Times More Fuel Than Claimed

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Fraunhofer ISI, in collaboration with the Öko Institute, released the results last week of a study it did of plug-in hybrid cars. That study came to the rather distressing conclusion that some PHEVs sold in Europe actually consume about three times as much gasoline as claimed. We will get into the details shortly, but at a time when everyone in the automotive world is running around like their hair is on fire to get more plug-in hybrids into showrooms, the reality is that many consumers are not getting what they paid for and government regulators are being bamboozled once again.

Is this a reprise of the great diesel cheating scandal that wracked the industry in 2015? Volkswagen was the public face of that slow-motion trainwreck, but several other manufacturers were complicit, including Bosch, which supplied many of the diesel fuel injection systems that enabled the cheating.

The Fraunhofer Report

The report, replete with many charts, tables, and graphs, is 61 pages long, and you are welcome to read it yourself. Dated February 18, 2026, it begins this way:

Plug-in hybrid vehicles (PHEVs) can be driven using either a combustion engine or battery-electric and can be charged via the power grid. These vehicles only offer climate benefits over conventional combustion engines when operating in battery-electric mode. PHEVs contribute significantly to European car manufacturers’ compliance with CO₂ fleet targets in Europe, but their real-world CO2 emissions are three to five times higher than the type-approval values, as shown by recent evaluations of real-world consumption data (On-Board Fuel Consumption Monitoring (OBFCM) data) from approximately one million PHEVs in Europe.

This study analyzes the regulatory implications of these deviations. Realistic values are derived for the so-called utility factor (UF), which combines the standard consumption values collected during type-approval with the combined consumption value. Furthermore, current suggestions by the German car makers association (VDA) regarding the regulatory treatment of PHEVs are evaluated and a scenario analysis is used to show the climate policy consequences that would result from the implementation of these demands. The aim is to create an evidence-based reference for political decisions on the further development of PHEV regulation.

To save you the drudgery of plowing through this massive report, The Guardian has done that for us. It says the study shows that PHEVs sold in Europe (remember, we are talking about more than 1 million vehicles in this study) burn an average of six liters of fuel per 100 km — about three times more than previously claimed.

“The scientists of the Fraunhofer Institute found that the main reason for the higher fuel usage was due precisely to the fact that the PHEVs use two different modes — the electric motor and the combustion engine, switching between both. Until now it has been claimed by manufacturers that the vehicles used only a little or almost no fuel when in the electric mode. The studies showed that this was not in fact the case,” The Guardian says.

Patrick Plötz of the Fraunhofer Institute told German broadcaster SWR they suspect the combustion engine in PHEVs is triggered to turn on far more frequently than previously thought. German-manufactured PHEVs were among those with the highest average fuel consumption, with the high-end Porsche model performing worst. He urged regulators to use the real-world emissions data rather than the figures submitted by the manufacturers. “Then one could say a manufacturer who does not comply with the (emissions) limits on the road may have to pay a penalty,” he said.

Non-German PHEVs Perform Better

In the study, the lowest fuel consumption levels were found in the less expensive PHEVs from Kia, Toyota, Ford and Renault, which typically consumed less than one liter per 100 km. By contrast, PHEV models from Porsche consumed 7 liters per 100 km. Oh dear, isn’t Porsche part of Volkswagen Group? Did those people learn nothing from Dieselgate?

Asked by SWR to explain the discrepancy, Porsche referred to “differing usage patterns,” which it said influenced fuel consumption. Porsche insisted its fuel consumption measurements were in line with legal requirements.

“The fuel consumption figures of our vehicles are based on the legally prescribed EU measurement procedures,” which ensured “uniform and comparable values across Europe. Deviations from individual real world consumption figures can arise due to different usage profiles and external conditions,” such as road conditions, or driver behavior, the company said.

What Is A PHEV?

How to decode this techno-speak? CleanTechnica readers, being well above average, know that PHEV is an acronym that covers many different propulsion systems. In some, the onboard internal combustion engine is there for one purpose and one purpose only — to spin a generator that supplies electricity to the traction battery. It is not mechanically connected to the wheels of the car — although, in some cases there is a “limp home mode” that allows the driver to get to safety in the event of a total failure of the electric powertrain.

In far too many cases, however, the engine is called up to power the wheels in many driving situations — accelerating away from a stop sign, getting over a speed bump in a mall parking lot or up a small hill, passing a car on the highway, or providing heat to the interior on a frosty day. In the case of Porsche, the brand is focused on performance, which means robust acceleration in all situations. Perhaps the engineers in Weissach are just trying to keep their customers satisfied?

Based on their finding, the Fraunhofer scientists are calling on EU regulators to adjust their measurements to fit the real-world findings, which would require stricter standards for how fuel consumption of plug-in hybrids is measured. They claim that change is urgently needed. Asked for a comment, the German Association of the Automotive Industry said it believed the existing methods for determining fuel consumption and CO2 emissions were reliable.

Cheating Is A Way Of Life

Regulators typically are policy wonks whose idea of a great car is a 2010 Toyota Corolla. They set the standards and the automakers immediately begin looking for work-arounds. Back in the days when people actually cared about fuel economy (many readers weren’t yet born that long ago), European manufacturers were famous for going to extraordinary lengths to boost the mileage of their cars.

In official tests, they used specially modified production models that used tires inflated until they were rock hard with shaved tread to reduce rolling resistance. Another favorite trick was radically altering the timing to favor efficiency over power. Some companies actually fitted these cars with special brakes that left extra clearance between the pads and the rotors to eliminate friction. It also made the brakes virtually useless. Windshield wipers were removed and panel gaps were sealed with clear tape.

The result was mileage claims that could never be achieved in real-world driving, unless you were going downhill in the Alps. The cars, as modified, were supremely dangerous to drive, with toe-in on the front wheels set to zero, but the manufacturers got the results they desired for their advertising programs. That’s what happens when regulators know nothing about what they are regulating.

The ultimate example of cheating happened when Smokey Yunick showed up at a NASCAR race with a car that was an exact replica of a production model but reduced in every dimension by 0.125 percent. The car looked like a production car but was just a tiny bit smaller in every aspect. It took NASCAR a while to catch on, but when it did, it started measuring every car with body templates that matched the production cars precisely.

The issue really is not about cheating, it is about regulations that are not matched to real-world driving conditions. If you conform precisely to the regs, you can’t actually be cheating, can you? What is needed more than anything is an education protocol for drivers and regulators that explains the difference between a series hybrid, a parallel hybrid, and an extended range EV. If consumers and regulators are confused, that creates a perfect opportunity for manufacturers to take advantage of any gaps in the rules they can find.

If there is a lesson here, it is that many so-called plug-in hybrids are not quite what they appear to be. Shame on manufacturers for playing games with regulators and the buying public and shame on consumers for not doing their due diligence.

Another factor in Europe is that many new cars are not purchased by private owners. They are company cars that are an integral part of executive compensation packages. Employers buy so-called plug-in hybrids to satisfy the regulators, but the drivers never plug the cars in because their employers reimburse them for gasoline but not for the cost of electricity.

The upshot is, there are many factors that combine to create the distortions the Fraunhofer researchers found and only some of them are attributable to manufacturers bending the rules in their favor. To escape the trap of cars that appear to be one thing on paper but are something else entirely out in the real world, we need better regulations that capture the entire driving experience. Dumb regulations are the devil’s plaything.

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