Can Diesel Engines Survive the 21st Century? It All Depends on Integrity

2023 ram 2500 heavy duty rebel
The Future of Diesel Engines Is In JeopardyStellantis
  • Dieselgate started back in 2014, but it has never really ended, as more and more allegations roll in of defeat devices across the diesel spectrum.

  • From VW and Daimler to Cummins and Bosch, the EPA, CARB, and the DOJ have slapped historic fines on manufacturers as recently as 2023.

  • As diesel engines begin to phase out, the few remaining from Ford and GM will be judged on their integrity of emissions compliance above all else.

Like millions of other Volkswagen TDI owners, I have a personal connection to what we now know as Dieselgate. Gripping the three-spoke steering wheel in my mom's turbodiesel Jetta SportWagen, I was intent on driving every single hour required under Oregon's Provisional Instruction Permit driving program.


It wasn't the Miata I really wanted and wasn't equipped with a manual transmission like my 1991 Saab 900 Turbo, but its 236 lb-ft of torque may as well have been Tesla Plaid levels of power to my juvenile senses.

diesel volkswagen and audi vehicles that vw bought back from consumers sit in the parking lot of the pontiac silverdome
In the wake of Dieselgate, nearly 600,000 Volkswagen TDI models were affected, with hundreds of thousands bought back by VW. AFP Contributor

Two months after being permitted, the sprawling emissions scandal that we now know as Dieselgate broke, and the family gem of a station wagon was bought back by its creator not long after that. Ultimately, it was a small price for my family to pay in the name of a cleaner future, unlike the nearly $35 billion in fines and settlements that Volkswagen has paid to the same effect.


But it wasn't just Volkswagen that was complicit. Since that shocking 2015 announcement, Dieselgate has dragged on, encompassing parts suppliers, commercial operators, and legacy domestic manufacturers. From Daimler and Bosch to Stellantis and Cummins, the proliferation of diesel cheat devices was not a few-bad-apples incident.

The latest example of this came late last year, as diesel technology developer Cummins agreed in principle to pay a $1.675 billion fine for its role in installing emissions defeat devices on nearly one million diesel Ram pickup trucks. This comes after Fiat Chrysler Automobiles (now Stellantis) pleaded guilty to emissions fraud for the same models in 2022.

Largest fine in history

This $1.675 billion fine is the largest civil penalty ever secured under the Clean Air Act, and it's going to get even more expensive for Cummins in the coming months. In addition to civil fines, Cummins is on the hook for $325 million worth of pollution remedies, bringing the bill to around $2 billion for the Indiana-based company.

This monetary fumble is only half of the trouble ahead for Cummins, as engine customer Stellantis is likely giving Cummins an earful. That's because 630,000 diesel-engined Ram 2500 and 3500 Heavy Duty models will soon be recalled to remove the emission defeat devices, according to the Associated Press.

the 2019 ram 2500 hd offers two engines a 64 liter hemi or a 67 liter cummins diesel
The 6.7-liter Cummins diesel offered up to 1000 lb-ft of torque in 2019.Stellantis

Cummins has remained insistent that there is no evidence of bad faith actions, making an official statement on its financial obligations late last week."We are looking forward to obtaining certainty as we conclude this lengthy matter and continue to deliver on our mission of powering a more prosperous world," the statement reads.

More fines coming?

In addition to the 630,000 trucks set for recall, the Environmental Protection Agency, California Air Resources Board (CARB), and Justice Department alleged that roughly 330,000 more trucks (model year 2019 through 2023) were equipped with undisclosed emissions control software.

Cummins says that punishment for the unreported software has already been included in previous penalties. Even so, U.S. Attorney General Merrick Garland said that the emission-bypassing engines emitted "thousands of tons of excess emissions of nitrogen oxides" over the years.


Why are diesel engines so different than traditional gasoline-powered engines? The scientists at CARB were more than happy to explain, but ultimately it comes down to a higher compression ratio, higher combustion temperature, and a leaner air-fuel ratio.

"NOx is produced by this high-temperature combustion and as a result, diesel engines inherently have higher NOx emissions," a representative from CARB explained in an interview with Autoweek. "In addition, the combustion of diesel produces diesel particulate matter, a known carcinogen, which is not an issue for gasoline engines."

2016 nissan titan xd 5 liter cummins v8 diesel engine
Cummins and Nissan also had a short-lived turbodiesel collaboration which resulted in a $59 million recall on Titan pickup trucks.Nissan

Additionally, traditional three-way catalysts produced for gasoline engines don't work for diesel engines due to the high levels of particulate that diesel engines produce. Instead, diesel-powered vehicles are equipped with control technologies like engine gas recirculation, diesel particulate filters, diesel oxygen catalysts, and selective catalytic reduction systems to fully treat diesel exhaust.

"These add cost and complexity as each component has its own optimal conditions. SCR systems need to reach a high temperature before being fully effective and DPFs need to reach a high temperature regularly to regenerate or have an active regeneration design," the folks at CARB explained.


With the proliferation of cheat devices amongst automakers like Volkswagen and Daimler and parts manufacturers like Bosch and Cummins, it's only natural to wonder about the future of diesel engines as a whole. And this is where things get complicated, as domestic manufacturers rely on diesel engines for a portion of heavy-duty pickups.

2018 ford f150 superduty

"Ford F-Series Super Duty trucks are for heavy-duty vocational and recreational customers who do everything from building, plowing, taking patients to the hospital, and towing heavy trailers and RVs. The Ford-designed and assembled Power Stroke V8 diesel delivers powerful performance, capability, and efficiency for these customers that hybrids and EVs simply can't answer yet," representatives for Ford said in a statement to Autoweek.

"Until alternate fuel technology is ready to meet the needs of Super Duty customers, we'll continue to offer Power Stroke diesels while meeting regulatory requirements, as we always do," the statement reads.


Ford hasn't been immune to litigation around diesel emissions, either, but the 2018 class-action lawsuit brought against Ford and its 6.7-liter Power Stroke diesel V8 was ultimately dismissed with prejudice by a federal judge in 2022. The same is true for General Motors, which was accused of diesel emissions fraud on its Chevy Cruze in 2016 before a federal judge dismissed the case with prejudice, citing a lack of evidence.

2021 gmc yukon denali with the 30l duramax turbo diesel
A 2021 GMC Yukon Denali with the 3.0-liter Duramax turbodiesel engine. Jim Frenak-FPI Studios

Employing a 6.6-liter turbodiesel V8 since 2001 and releasing a 3.0-liter turbodiesel inline-six back in 2019, GM's Duramax lineup is perhaps as iconic in the diesel scene as Cummins products. Available on the Silverado, Suburban, and Tahoe, the 3.0-liter Duramax engines went through significant developments to keep them emissions-compliant from the jump.

Continuous improvements...

"The ability to meet emissions and increase power is primarily due to improvements in the combustion system (new pistons, fuel injectors), improvements to the fuel system (higher fuel pressure from 2000 bar to 2200 bar), and improvements to the turbocharger (improved compressor efficiency)," said a spokesperson for Chevrolet's Truck division in a statement to Autoweek.

2001 chevrolet silverado hd one ton pickup with duramax 66l turbo diesel v 8 engine, rated at 520 lb ft of torque
The 6.6-liter Duramax turbodiesel V8 was launched with the 2001 Chevrolet Silverado, making 520 lb-ft of torque.Chevrolet

Since its launch over 20 years ago, the 6.6-liter V8 has also undergone significant upgrades, seeing as the engine is in its seventh generation. Most recently, GM says it improved the washcoat inside its diesel oxidation catalyst (DOC), a diesel-specific form of catalytic converter. a point

Such extensive work to keep diesel derivatives alive may soon be futile, as cities across the globe and California begin to crack down on diesel models. Paris, Mexico City, Madrid, and Athens have previously committed to banning diesel cars from their city centers by 2025, and California isn't far behind.

After EPA approval earlier in 2023, California will begin phasing out the sale of new, commercial diesel trucks this year, eventually aiming for a zero-emissions sales mix of up to 75% by 2035. Ultimately, California could outright ban the sale of commercial diesel trucks by 2036 and aim for all commercial vehicles to be zero emissions by 2042.


"Renewable and biodiesel are both viable alternatives to fossil fuels, as are electricity and hydrogen. CARB regulations, specifically the Low Carbon Fuel Standard, create a growing market for these much cleaner, and zero-emission alternatives," a representative for CARB explained in an email with Autoweek.

us carbon emissions dropped nearly two percent in 2023

What does this mean for regular, diesel passenger vehicles before 2035? It's not clear just yet, but GM says it isn't too worried about the future of diesel models. With so many of its eggs in the electric basket, GM is hoping to be trending in the right direction by then.

Multi-pronged approach

"General Motors and California have a shared vision of an all-electric future and eliminating tailpipe emissions from new light-duty vehicles by 2035. California's regulatory programs for medium- and heavy-duty trucks allow for an orderly transition for GM and other automakers so we can continue to meet market needs. We look forward to working with California, as well as the other states, localities, and the federal government on complimentary policies to achieve this shared vision," representatives for GM said in an email to Autoweek.

Even as diesels die off in front of us, manufacturers must produce the remaining years of turbodiesel trucks with integrity. With the transportation sector responsible for one-third of US greenhouse gas emissions and the accompanying public health impacts continuing to grow in severity, a cleaner future is non-negotiable.

Were you impacted by Dieselgate? How did your car ownership change as a result? Please share your thoughts below.