DTNA releases DEF DeRates software update

Daimler Trucks North America is releasing a software update that includes revised diesel exhaust fluid induction parameters, which will increase the minimum speed before work will begin.

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.

There are built-in safeguards on induction trucks and tractors that ensure that the emissions system works properly by cutting down on vehicle speed and power should problems be detected.

The deceleration prompts the driver to correct the problem, usually refilling the DEF tank, repairing a faulty sensor or component, or performing a regeneration cycle.

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

The updates are scheduled to continue throughout 2026.

Updates are optional and must be done with an on-site hard plug-in using the Diagnostics link.

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

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

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

If the tank remains empty at the end of that distance or time, engine torque is reduced by 30% until the next 4,200 miles or 80 hours of engine operation have passed.

Additionally, an engine management system kicks in to limit the speed by 25 mph until 8,400 miles or 160 engine hours have passed.

Previously, a truck or tractor in the final stages of deceleration was limited to 5 mph and could not restart once stopped.

DTNA’s updated program was welcomed by the Federal Government.

“For too long, small businesses like farmers, truck drivers and construction workers have borne the costs of unreliable DEF systems through costly repairs and unnecessary downtime. That’s why SBA is calling on OEMs to implement the recent EPA guidance,” said Small Business Administrator Kelly Loeffler.

Loeffler said, “SBA welcomes Daimler Truck North America’s decision to equip vehicles with updated DEF induction software, which is a common-sense move that provides operators with greater reliability while reducing costs. This is exactly the kind of relief most hard-working Americans deserve.”

The SCR technology and DEF requirement were introduced to meet the 2010 model-year EPA mandate. DEF is a non-toxic, colorless and odorless solution consisting of 32.5% urea and 67.5% deionized water.

Industrial urea manufacturing involves the chemical reaction of ammonia and carbon dioxide, with the most cost-effective method using natural gas as a feedstock. As a result, major production centers include the US Gulf Coast and the Middle East.

However, in March, the EPA approved a guidance update that will allow truck manufacturers to replace the urea quality sensor with a nitrogen oxide sensor.

win march update American Trucking Association Support.

“As we have said before, these systems have often sidelined safe, compliant trucks due to faulty or unreliable DEF quality sensors, a problem that has been exacerbated by massive parts shortages in recent years,” Patrick Kelly, ATA’s vice president of energy and environmental affairs, said in a statement. “When a malfunctioning sensor can trigger full throttle, the result is unnecessary downtime, unnecessary towing costs, strained supply chains and higher costs across the board.”

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

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

Freightliner achieved 35.3% share of the Class 8 retail sales market in 2025, up from 36% in 2024, as the brand’s sales fell 14.9% to 73,585 trucks in 2024 from 86,470. Western Star increased its stake in the pie from 4.8% in 2024 to 5.5% in 2025, subject to the total sale. 11,461 trucks.