Overview:

• Deleting or tampering is still illegal everywhere. The Clean Air Act bans removing or disabling emissions controls and bans defeat devices for on-road and nonroad engines, including any nonroad engine subject to federal regulations. See 42 U.S.C. § 7522 and 40 CFR 1068.101, plus EPA’s tampering policy. USC § 7522 • 40 CFR 1068.101 • EPA tampering policy PDF
• The 2010 soot and NOx limits still apply. Heavy-duty diesels must meet 0.01 g/bhp-hr PM and 0.20 g/bhp-hr NOx. These drove DPF and SCR adoption and were phased in 2007 to 2010 (with phase-in periods based on model year and engine type). They have not been repealed. 40 CFR 86.007-11 • DieselNet summary
• 2025 actions targeted GHG programs and California-only waivers, not deletes. On June 12, 2025, three Congressional Review Act resolutions voided EPA decisions granting California waivers for ACT, ACC II, and the Heavy-Duty Omnibus. Separately, on July 29, 2025, EPA proposed rescinding the 2009 GHG Endangerment Finding for vehicles and removing federal GHG tailpipe standards. None of that legalizes deletes or touches the 2010 soot and NOx limits. White House statement, 6/12/25 • H.J.Res.87 • H.J.Res.88 • H.J.Res.89 • EPA proposal page • Federal Register, 8/1/25

Myths About Recent Diesel Emissions Rule Changes

“Trump scrapped all diesel emission rules. I saw it on Facebook and TikTok. I even saw a guy on YouTube saying I can delete my DPF and not get into any trouble at all.”

Facts on Trump’s Diesel Emissions Rule Changes

1)What diesel emissions regulations say about tampering and deletes

The Clean Air Act bans:

• Removing or rendering inoperative emissions controls on any applicable engine or vehicle covered by federal regulations.
• Making, selling, offering, or installing defeat devices.

These prohibitions apply to all engines sold or operated in the United States, as defined by federal regulations.

Violations bring civil penalties, and knowing conspiracies can trigger criminal liability. Primary sources: 42 U.S.C. § 7522 • 40 CFR 1068.101 • EPA Enforcement Policy

2) The 2010 baseline still rules your truck

The 2007 to 2010 heavy-duty program locked in 0.01 g/bhp-hr PM and 0.20 g/bhp-hr NOx emission standards. That is why modern trucks have DPF, EGR, and SCR—these systems are equipped to reduce exhaust emissions and meet strict emission standards. These limits remain in force. 40 CFR 86.007-11 • DieselNet

What g/bhp-hr meansIt is a rate limit: grams per brake horsepower per hour. As engine work increases, the allowed grams scale with work, but the rate stays capped. The expected result of these requirements is a significant reduction in exhaust emissions, particularly particulate matter captured by the diesel particulate filter.

3) What actually changed in 2025

• California waivers: CRA disapproved EPA waiver decisions for ACT, ACC II, and the Heavy-Duty Omnibus. Implementation of new standards often varies by model years, with each decade bringing updated requirements. That blocks those California-only programs unless courts reverse it, but it does not change federal soot and NOx limits or the anti-tampering ban. White House, 6/12/25 • H.J.Res.87 • H.J.Res.88 • H.J.Res.89
• Federal GHG rules: Additionally, EPA proposed rescinding the vehicle GHG Endangerment Finding and removing GHG tailpipe standards. It is not final. As usual, any deregulation has to go through a formal process before going into effect. This includes a public hearing process, which we can expect to be heated. It’s also reasonable to expect this to be handled in court, which will also delay any actual changes. Soot and NOx rules and tampering prohibitions are separate and remain regardless. EPA proposal • Federal Register notice

Context: The 2009 Endangerment Finding stems from Massachusetts v. EPA (2007) and is the legal basis for regulating vehicle GHG. EPA is now seeking to overturn it for mobile sources. That fight is ongoing and will take time. None of that authorizes deletes. Massachusetts v. EPA overview • EPA Endangerment Finding page

4) California air resources board’s Clean Truck Check is real today

If you run in California with a highway vehicle or as part of the trucking industry, the Clean Truck Check (HD I/M) program requires reporting and periodic emissions testing, with registration holds and enforcement through CARB’s database. Roadside tech screens for high emitters and triggers test orders. Other states are studying similar tools.

These efforts are designed to improve safety and compliance across the trucking industry.

CARB Clean Truck Check overview • CARB compliance and testing timing

5) Roadside enforcement and out-of-service risk

• CVSA’s Out-of-Service Criteria allow inspectors to sideline vehicles for critical defects until corrected, and FMCSA requires repairs before returning to service. CVSA OOSC overview • 2025 OOSC announcement
• What draws attention: straight pipes in place of aftertreatment, cut or unplugged sensor harnesses, and heavy soot deposits on the tailpipe or stack that are easy to see. Those signs can trigger a deeper inspection, a process that may also assess whether modifications have increased engine power or produce excessive emissions, and, where CARB or state programs apply, emissions citations or test orders. CARB program page

6) Recent penalties that actually happened

• PPEI and Kory Willis:—a manufacturer of tuning software—guilty pleas, December 18, 2024 sentencing. Joint $1.55 million criminal fine, probation, and $3.1 million total fines and civil penalties. DOJ press release • Earlier DOJ plea
• Elite Diesel Service (CO): December 9, 2024 sentencing for conspiracy to violate the Clean Air Act by disabling monitoring components on hundreds of trucks. DOJ Colorado • ENRD bulletin
• Rudy’s Performance Parts: 2024 civil penalty $7 million under consent decree, with separate criminal case elements. EPA and DOJ coverage

7) Diesel exhaust fluid (DEF) is still not “cow piss”

Diesel Exhaust Fluid is 32.5% high-purity urea in deionized water, standardized under ISO 22241 for SCR systems. EPA updated inducement guidance in August 2025 to reduce abrupt derates while still forcing timely repairs. Using off-spec fluid risks catalyst damage and compliance problems.
ISO 22241 definition • EPA DEF guidance fact sheet • DieselNet summary • 40 CFR 1036.111 inducements

Click here to watch Jim from DPF Guys explain how DEF isn’t pee in this popular YouTube video.

8) A CO₂ fact drivers actually ask about

A gallon of diesel weighs about 7 pounds, yet burning it produces about 22.45 pounds of CO₂ because the carbon in the fuel bonds with oxygen from the air. This is why GHG rules track fuel use. It does not change your DPF obligations.

Check out the EIA emissions coefficients: This calculation is important for understanding the impact of transportation and car emissions on overall greenhouse gas inventories.

Improving Fuel Efficiency: What Matters and What Doesn’t

When it comes to diesel engines, improving fuel efficiency isn’t just about saving money at the pump—it’s also a key strategy for reducing diesel emissions and staying compliant with diesel emissions regulations. The Environmental Protection Agency (EPA) has set clear standards to reduce emissions, and many of the best practices for fuel efficiency go hand-in-hand with meeting these requirements.

One of the most effective steps is using ultra low sulfur diesel. This cleaner fuel dramatically lowers sulfur content, which helps reduce emissions and keeps aftertreatment systems like diesel particulate filters (DPF) and selective catalytic reduction (SCR) working properly. Technologies such as exhaust gas recirculation (EGR) and diesel exhaust fluid (DEF) are also essential. EGR helps lower nitrogen oxides (NOx) by recirculating a portion of the exhaust back into the engine, while DEF is used in SCR systems to break down NOx into harmless nitrogen and water.

It’s important to note that shortcuts like DPF deletes not only violate EPA regulations but can actually hurt your fuel efficiency and increase emissions. Removing emissions controls often leads to higher soot buildup, more frequent maintenance issues, and potential legal trouble. Instead, regular maintenance, using the right fuel, and keeping emissions systems in good working order are the proven ways to improve fuel efficiency and reduce emissions. The bottom line: follow the EPA’s guidance, use compliant fuels and fluids, and avoid illegal modifications to keep your diesel engine running clean and efficient.

The Environmental Impact of Diesel Emissions

Diesel emissions have far-reaching effects on both the environment and public health. Diesel engines release pollutants such as nitrogen oxides (NOx), particulate matter (PM), and carbon dioxide (CO2), all of which are regulated under emissions standards set by the EPA and, in California, by the California Air Resources Board (CARB). These emissions contribute to poor air quality, smog, and the formation of ground-level ozone, which can harm crops, forests, and water sources.

The health impacts are just as serious. Exposure to diesel emissions is linked to respiratory illnesses, cardiovascular disease, and even premature death, especially in communities near highways, ports, and industrial areas. Particulate matter from diesel exhaust can penetrate deep into the lungs, while NOx emissions contribute to the formation of acid rain and further degrade air quality.

Reducing diesel emissions is critical for protecting human health and the environment. That’s why strict regulations and emissions standards are in place for diesel engines, and why agencies like the EPA and CARB continue to push for cleaner technologies and fuels. By following these regulations and maintaining your diesel equipment, you’re not just ensuring compliance—you’re also helping to safeguard air quality and public health for everyone.

Tech Advancements: What’s New and What’s Hype

The diesel industry is constantly evolving, with new technologies emerging to help fleets and manufacturers meet ever-tightening emissions standards and improve fuel efficiency. One of the most impactful advancements is the adoption of selective catalytic reduction (SCR) systems, which use diesel exhaust fluid (DEF) to reduce NOx emissions by up to 90%. This technology has become standard on most new heavy-duty trucks and is a cornerstone of modern emissions compliance.

Another promising area is the development of advanced engine designs, such as homogeneous charge compression ignition (HCCI) engines, which aim to combine the efficiency of diesel with even lower emissions. These innovations, along with improvements in aftertreatment systems and onboard diagnostics, are helping fleets achieve better fuel efficiency while staying within EPA and CARB regulations.

However, not every new gadget or modification lives up to the hype. For example, DPF deletes are often marketed as performance upgrades, but in reality, they are illegal in most cases and can lead to higher emissions, increased maintenance costs, and significant penalties. The EPA and other agencies regularly update fact sheets and guidance to help manufacturers, fleets, and shops ensure compliance and avoid costly mistakes.

When evaluating new technologies, it’s essential to rely on proven systems that are approved by regulatory agencies and supported by real-world data. Staying informed through official EPA resources and industry updates is the best way to ensure your fleet remains compliant, efficient, and ahead of the curve.

What This Means for Drivers, Fleets, and Shops

• If you delete, you own the risk. Federal anti-tampering law is unchanged. The 2010 soot and NOx limits still apply. California’s Clean Truck Check is active and uses roadside screening. Inspectors can place you out of service for critical defects until fixed. 42 U.S.C. § 7522 • 40 CFR 86.007-11 • CARB Clean Truck Check • CVSA OOSC
• If you run a shop, the target is on you too. Manufacturing, selling, or installing defeat devices is a fast track to fines, probation, and sometimes custody. The recent cases above are court outcomes.
• If you want to stay productive, keep aftertreatment working. DPF cleaning and SCR diagnostics cost less than downtime, citations, and legal bills. Some grants and funding programs are available to help cover the cost of maintaining or replacing your filter and other emissions equipment.

FAQ Quick Hits

• Were the 2010 soot and NOx limits repealed? No. They remain the nationwide floor for all affected model years. 40 CFR 86.007-11
• Are GHG rules gone? Not today. EPA proposed rescinding the Endangerment Finding for vehicles and removing GHG tailpipe rules. That proposal is not final. Separately, Congress voided certain California waivers using the CRA. Neither action legalizes deletes. EPA proposal • White House, 6/12/25
• Do these rules apply to light duty vehicles? No, these rules primarily target heavy-duty vehicles. Light-duty vehicles, such as passenger cars and small trucks, are subject to separate EPA standards and regulations.
• What is the Energy Policy Act and how does it relate to diesel emissions rules? The Energy Policy Act authorized funding and programs to reduce emissions, including grants and regulatory initiatives that support advancements in diesel emission standards.

A Short Note on Enforcement Tech in the News and on the Rise

• California Clean Truck Check requires testing and uses roadside screening to find high emitters. CARB overview • Testing schedule
• Remote sensing and plume-capture pilots are already in use to identify likely violators while in motion and to route them to testing. Examples include CARB’s PEAQS pilots with license plate capture. CARB media advisory • Technical brief

Similar enforcement technologies may be implemented for marine engines in the future as regulations expand.