EPA Eases Rules On Diesel Exhaust Fluid Systems

The U.S. Environmental Protection Agency (EPA) has issued updated voluntary guidance for model year 2026 and older diesel engines and equipment, allowing manufacturers to revise their Diesel Exhaust Fluid (DEF) system software to adjust SCR related inducements.

Diesel selective catalytic reduction (SCR) technology reduces NOx emissions and relies on the injection of urea (also known as “diesel exhaust fluid”, “DEF”, or other trademark names) as part of the emission control system.  If the system runs out of Diesel Exhaust Fluid, NOx emissions can increase, exceeding federal standards. EPA mandates that manufacturers must have an “inducement” strategy to ensure that vehicle operators do not operate the vehicle without sufficient urea in the emission control system and/or prevent tampering. 

In the past, the EPA required inducement systems to kick in relatively quickly and to severely limit vehicle operation. Generally, vehicle operators have a four-hour window before operation would be limited to 5 mph after safe harbor conditions are met. This regulation was seen as too restrictive and even unsafe at times, since it did not provide enough time or power to get off rural roads or handle steep grades at higher elevations while finding a service center. All RVers are encouraged to continually monitor their Diesel Exhaust Fluid levels to ensure adequate amounts.

Under the newly released guidance, voluntary inducement strategies can begin over a much longer time frame and will allow for a higher speed.  For heavy-duty trucks and RVs, inducement strategies are phased in over three intervals with modest reductions during the first two intervals. The final interval begins after 8,400 miles (or 160 hours) and limits the engine to 25 mph. 

The EPA has stated that this change maintains environmental protection while giving vehicle operators more flexibility on the road. For model year 2027 and newer engines, EPA published new emission standards in 2023 that mandate engine manufacturers incorporate more lenient inducement strategies, similar to the recent guidance.

The RV Industry Association will continue to provide updates as more information becomes available.

For more information, see the EPA’s website.

The guidance document is available here.