Diesel Trucks with Gen5 DD15 Engines Plagued by Calibration Defect, Class Action Lawsuit Claims

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A proposed class action lawsuit alleges that diesel trucks equipped with a Gen5 DD15 engine produced between certain dates are plagued by an engine calibration defect that causes the vehicles to generate more soot, reducing engine performance and causing premature degradation of certain emissions systems.

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The 82-page complaint contends that defendants Daimler Truck North America (DTNA), Detroit Diesel Corporation and Western Star Truck Sales have failed to disclose that the apparent engine calibration defect affecting nearly 200,000 heavy-duty diesel trucks can cause accelerated particulate matter buildup within the trucks’ diesel particulate filter (DPF), necessitating the DPF to undergo more high-temperature regeneration cycles that prematurely degrade the vehicles’ emissions aftertreatment systems.

According to the automotive lawsuit, the aftertreatment system is designed to reduce or eliminate harmful emissions and consists of a diesel oxidation catalyst, particulate filter and selective catalytic reduction (SCR). Per the case, as soot accumulates in the DPF, the engine needs to work harder to expel exhaust through the tailpipe. Once accumulated soot reaches certain levels, the DPF must be renewed through a process known as regeneration, the case shares.

The filing says that the thermal stress and excessive heat from repeated regeneration cycles cause cumulative damage to the DPF and related components. On July 22, 2025, DTNA initiated a field service campaign to address the engine calibration defect, but the case says that the remedy—reprogramming of the trucks’ motor control module—did not provide a repair for DPFs that had already begun to degrade or prematurely age.

In fact, the case states that the new calibrations provided by the field service campaign may have had a detrimental impact on the trucks’ fuel economy and resulted in higher operating costs for businesses using them for long-haul trips. The case says that operating costs—e.g., fuel costs—are “obviously” of the utmost importance to trucking companies.

Moreover, the complaint asserts that the field service campaign was inadequate because it did not provide evaluations for damage sustained by DPFs, SCRs, or related emissions-control components, nor did it restore damaged components to their expected service life or offer an extended warranty.

Per the filing, the defendants represent in advertising and marketing materials that the DD15 engines are reliable and durable, highlighting the “big selling point” that the engines can provide up to three percent better fuel economy than previous iterations.

“Even if the [c]ampaign’s reduction in fuel economy proves modest, any decreases in fuel efficiency translate into substantial increases in operating costs over hundreds of thousands of miles these working trucks are driven in their lifetimes,” the lawsuit stresses.

As an example, the suit relays that a long-haul trucker with a DD15-powered engine covering 100,000 miles per year would incur an additional $1,400 per year in operating costs even with a mere two-percent drop in fuel efficiency.

The filing states that trucks with the defectively calibrated engines include all that were equipped with a 2021-2025 Gen5 DD15 engine (model 472.912) produced between January 15, 2020 and February 21, 2025 (the class trucks).

The Daimler Truck North America class action lawsuit looks to cover all individuals and entities who purchased or leased a class truck in the United States or its territories.

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