DTNA Rolls Out DEF Derates Software Update

A fifth-generation Freightliner Cascadia. (Daimler Truck North America)

Daimler Truck North America is rolling out a software update that incorporates revised diesel exhaust fluid inducement parameters, lifting the minimum speed before work must be carried out.

The update follows revised guidance from the Environmental Protection Agency in August.

Selective catalytic reduction technology uses DEF to convert nitrogen oxides into nitrogen and water, supporting compliance with EPA emissions standards.

Inducements are the built-in safeguards on trucks and tractors that ensure emissions systems function appropriately by cutting vehicle speed and power should issues be detected.

The slowdown “induces” the driver to correct the issue, typically by refilling the DEF tank, repairing a faulty sensor or component, or performing a regeneration cycle.

DTNA began rolling out the update in February for about 330,000 in-service vehicles with DD15 engines (model years 2021-2025) and DD13 engines (model years 2022-2025).

The updates are set to continue throughout 2026.

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A Detroit DD15 engine. (Daimler Truck North America) 

Updates are optional and must be carried out with an on-site hard plug-in using a diagnostic link.

Freightliner and Western Star vehicles equipped with Detroit engines are already shipping with the updated software.

Per the revised guidance, the speed limit in final inducement will be increased to 25 mph from 5 mph, and the time to reach final inducement for component-related issues will be extended.

Under the stages of inducement, initially when a truck runs out of DEF, its engine torque will be reduced by 15% for 650 miles or 100 hours.

Should the tank remain empty at the end of that distance or time, the engine torque is derated by 30% until another 4,200 miles or 80 hours of engine operation elapse.

Beyond that, an engine management system is triggered to limit speed to 25 mph until 8,400 miles or 160 engine hours pass.

Previously, a truck or tractor in the final stage of derating would be limited to 5 mph and would not restart once shut down.

DTNA’s update program was welcomed by the federal government.

“For too long, small businesses like farmers, truckers and construction workers have borne the cost of unreliable DEF systems through expensive repairs and needless downtime. This is why the SBA has been calling on OEMs to implement recent EPA guidance,” Small Business Administrator Kelly Loeffler said.

“The SBA welcomes Daimler Truck North America’s decision to equip vehicles with updated DEF inducement software, a common-sense step that gives operators greater reliability while reducing costs. This is exactly the kind of relief that the hardest-working Americans deserve,” Loeffler added.

SCR technology and the need for DEF was introduced to meet 2010 model-year EPA mandates. DEF is a nontoxic, colorless and odorless solution comprising 32.5% urea and 67.5% deionized water.

Industrial urea manufacturing involves the chemical reaction of ammonia and carbon dioxide, most cost-efficiently using natural gas as the feedstock for the former. As a result, key production centers include the U.S. Gulf Coast and the Middle East.

In March, though, EPA approved a guidance update that will allow truck manufacturers to replace urea quality sensors with nitrogen oxide sensors.

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The March update won American Trucking Associations backing.

“As we have previously said, these systems have too often sidelined otherwise safe, compliant trucks due to faulty or unreliable DEF quality sensors, an issue that was compounded by widespread parts shortages in recent years,” Patrick Kelly, ATA vice president of energy and environmental affairs, said in a statement. “When a bad sensor can trigger a full inducement, the result is unnecessary downtime, unnecessary towing costs, strained supply chains and higher costs across the board.”

U.S. Rep. Julie Fedorchak (R-N.D.) in early June introduced a bill in the House of Representatives to codify the March guidance, the Diesel Engine Flexibility Act.

DTNA is working with EPA to ensure its approach aligns with regulatory requirements while at the same time maintaining system performance and reliability, but it does not plan to remove DEF sensors from Freightliner or Western Star vehicles currently, a representative told Transport Topics on June 18.

Freightliner won a 35.3% share of the Class 8 retail sales market in 2025, down from 36% in 2024, as the brand’s sales fell 14.9% to 73,585 trucks from 86,470 in 2024. Western Star improved its share of the pie to 5.5% in 2025 from 4.8% in 2024, selling a total of 11,461 trucks.