No, DEF Isn’t Going Away, But Here’s What Will Change
The U.S. Environmental Protection Agency (EPA) recently issued new guidance that impacts every truck driver on the road. The new EPA rule for DEF systems intends to revise existing software in diesel trucks to prevent sudden, severe engine derates and shutdowns when a DEF system malfunction or low-fluid event occurs.
This change is not about lowering emissions standards, but about improving operational safety and efficiency for truckers. For professional drivers, this new guidance directly affects how they need to manage their Selective Catalytic Reduction (SCR) systems to prevent costly truck emissions failures and the dreaded derate truck scenario.
As an award-winning fleet committed to driver-centric solutions, Chief Carriers understands this new EPA guidance is a clear signal that the industry is moving toward a new standard for operational excellence, where proactive maintenance and immediate action are non-negotiable. We’ll walk you through the key aspects of the new rule and provide an actionable checklist to help you stay compliant, on the road, and earning.
Understanding the Derate Trigger: How a DEF System Malfunction Leads to Trouble
The SCR system, which uses Diesel Exhaust Fluid (DEF) to reduce harmful nitrogen oxide (NOx) emissions, is monitored by the truck’s onboard diagnostics (OBD) system. When an SCR system malfunction occurs, a chain reaction begins that can quickly sideline a truck.
If this system detects a problem—such as a faulty sensor, low DEF quality, or a contaminated tank—it triggers a fault code. This initial warning is a critical first step, and the danger lies in ignoring this initial alert.
Currently, when a DEF system malfunction occurs, a truck’s engine power can be severely limited or even shut down within a few hours of the initial warning. This sudden and often drastic response, known as a derate, is designed to ensure the truck remains emissions-compliant but can leave drivers stranded in unsafe locations or unable to complete a route.
Maybe some of you can relate. You’ve been running down the road, and all of a sudden, the check engine light pops on, or the DEF light pops on, and you know you’ve got a problem. You’ve got limited time before the truck derates and your speed drops.
-Andrew Winkler, General Manager of Chief Carriers
The New, Phased Derate Sequence
Instead of an immediate, drastic power reduction, the new rule introduces a multi-stage process that allows drivers to safely navigate a DEF system issue. The sequence of events that will now lead to a full derate scenario is as follows:
- Fault code activation: The onboard computer detects an issue, such as a DEF system malfunction, and logs a specific fault code.
- Warning lights: A “check engine” or DEF system warning light illuminates on the dashboard, signaling a problem to the driver.
- Initial derate: After a set period (e.g., 650 miles or 10 hours of operation), the engine’s torque is reduced by about 15%, giving the driver ample warning and time to address the issue without significantly impacting speed.
- Secondary derate: If the issue is not fixed after the first phase (e.g., after 4,200 miles), the engine will be derated further by 30%, which will likely impact the truck’s ability to maintain highway speeds on inclines.
- Final speed limitation: If the problem persists for an extended period (e.g., 8,400 miles), the truck’s speed will be limited to 25 mph, effectively forcing the driver to seek immediate repair.
This tiered approach is a key component of the new guidance and is designed to provide drivers with a much safer and more practical way to handle an emissions issue than previous rules, which could trigger a severe derate or shutdown in as little as four hours.
What the new rule says is, basically, they want the OEMs, the manufacturers, to change their software, change the programming in the truck so it’s not so unsafe—so that it’s not such a drastic drop in the speed of the truck.
-Andrew Winkler
The Proactive Driver’s Checklist: Preventing Costly Emissions Failures
For professional drivers, the best defense against truck derating and lowering emissions on diesel trucks is a strong offense. The new EPA rule on truck emissions makes a proactive approach essential for staying compliant and on schedule.
Here is a checklist for every driver to perform as part of their daily pre-trip inspection:
- Check DEF tank level: Ensure the Diesel Exhaust Fluid level is always above a quarter tank. Running low is the most common and easily preventable cause of a derate.
- Inspect DEF cap and seals: Look for any damage or signs of a loose cap. A loose cap can introduce contaminants or allow the DEF to evaporate, compromising its quality.
- Look for crystallized DEF residue: Crystallization around the DEF lines and fittings can be a sign of a small leak. This is a crucial visual cue that should be addressed immediately.
- Verify no warning lights: Before starting the trip, confirm that there are no active dashboard warning lights related to the truck’s DEF system or check engine lights.
RELATED: The True Cost of Trucking Safety: Why Prevention is Key
Choosing Your DEF
Not all Diesel Exhaust Fluid is created equal. Using the correct, high-quality DEF is crucial for the health of your SCR system. Always use DEF that is certified by the American Petroleum Institute (API), as this ensures the fluid contains the correct urea concentration (32.5%) and is free of harmful contaminants that can damage your system.
A Different Perspective: Why the EPA Rule Is a Win for Drivers
The new EPA guidance might seem like another regulatory hurdle, but it’s ultimately a significant win for drivers. The conventional wisdom is that stricter emissions rules create more potential for breakdowns and driver inconvenience. However, a different perspective suggests this new guidance is a move toward a more reliable, safer, and economically viable trucking environment.
By requiring OEMs to build in more flexible inducement schedules, the rule prevents the sudden and dangerous power loss that has historically left drivers stranded in unsafe locations or unable to make a delivery. The extended grace period for repairs allows drivers to finish their routes, find a safe service location, and get their DEF system malfunction fixed without an immediate, stressful derate.
We predict that this policy shift will lead to a decrease in roadside service calls related to DEF-system-induced breakdowns for commercial trucks. This new guidance ultimately protects drivers by ensuring better-maintained fleets, promoting road safety, and preventing unexpected breakdowns due to emissions failures.
The EPA is just trying to make it easier on you. So when something does malfunction, it doesn’t put you alongside the road disabled. You have time to think about it, react, schedule, get in a shop, and finish the load you’re on.
-Andrew Winkler
Proprietary Insight: The Chief Carriers’ Advantage
At Chief Carriers, we believe that an ounce of prevention is worth a pound of cure. Our commitment to driver success goes beyond mere compliance. Our proactive maintenance program is designed to prevent truck emissions failures before they ever occur, ensuring our drivers spend their time on the road, not in the repair shop.
“This is a smart, common-sense move by the EPA. We’re not rolling back clean air progress…we’re simply fixing one of the biggest headaches in trucking,” says Andrew Winkler, General Manager at Chief Carriers. “DEF systems have so many sensors that when one failed, you often had no choice but to tow a truck, wait on parts, and eat the downtime cost…all for what could be a simple sensor replacement. By phasing in the derates instead of shutting trucks down right away, drivers stay safer, fleets save money, and the industry as a whole wins.”
RELATED:Chief Carriers’ Truck Maintenance Tips: Keeping Your Flatbed Truck Rolling Strong
FAQ: Answering Your Top DEF System Questions
What does the new EPA rule say about DEF systems?
The new EPA rule on DEF system guidance encourages OEMs and manufacturers to revise the software in new and existing heavy-duty diesel engines. The goal is to provide a more flexible, multi-phased approach to engine derating, replacing the previous, often sudden and severe, power loss that occurred in cases of DEF system malfunction or low fluid levels. This allows drivers more time to address the issue before it impacts their operational capacity.
When does the new rule go into effect?
The new EPA rule goes into effect for Model Year 2027 and later heavy-duty trucks. For vehicles already in use, the EPA has issued guidance allowing manufacturers to make necessary software changes to the existing fleet to implement the new, more flexible derate schedule. This means that while new trucks will be built with this software, existing trucks can also be updated to meet the new standards, which prevents the sudden and severe derates that occurred under previous regulations.
Can I get fined for a DEF system malfunction?
Yes, if a vehicle is found to have a malfunctioning or tampered DEF system during a roadside inspection, it can result in significant fines and an out-of-service order. This is particularly true if the vehicle is operating in a derated state or if the emissions control system has been disabled or removed. The new EPA guidance does not change the fact that the driver and fleet are responsible for ensuring the vehicle is emissions-compliant.
How is a derate different from a normal engine slowdown?
A derate is a specific, computer-controlled reduction of engine power initiated by the ECU when it detects a fault in the emissions system. This programmed protective measure prevents the truck from operating in a high-polluting state. Unlike a general loss of power from a mechanical issue, a derate is a deliberate, regulatory-driven event.
What are the symptoms of a failing SCR system?
Common symptoms of a failing SCR system malfunction include a persistent check engine light or a semi-truck DEF system warning light, a visible loss of power, reduced fuel economy, or a noticeable increase in exhaust smoke. In more severe cases, you may see a crystallization of DEF fluid around the injector or hear an unusual hissing sound from the lines. These are all signs that the system is not working correctly and requires immediate attention.
RELATED: Repairs and Maintenance: Keeping Truck Fleets on the Road
Driving with Confidence in a New Era
By providing our drivers with the expertise and resources to prevent a DEF system malfunction and avoid a derate truck scenario, Chief Carriers isn’t just complying with regulations; we’re leading the way in professional driver care.
At Chief Carriers, we’re already ahead of this curve. Our commitment to rigorous maintenance, cutting-edge diagnostics, and unwavering driver support ensures that our drivers can focus on what they do best: delivering goods safely and efficiently. If you’re a driver looking for a company that prioritizes safety, apply with us today.
Hear more from our General Manager, Andrew Winkler, in the Driven Too Far podcast episode, “New EPA Rules and What They Mean for You.”
