Mack Trucks told federal safety regulators on Sept. 28, 2026 that 850 of its tractors may calculate axle loads incorrectly when they pull tank trailers, which can weaken the trailer brakes and lengthen the distance needed to stop. The trucks are 2026 and 2027 Mack Anthem and Pioneer models that were built with a tanker application package. The company’s remedy is a software update that switches off the calculation at the center of the problem.
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The recall is a precaution built on a software weakness, not a count of crashes. Mack’s filing reports no accidents or injuries tied to the issue, and it estimates that roughly 0.1 percent of the 850 trucks actually carry the defect. Every truck with the tanker package is swept in anyway, because the company selected the population from its manufacturing records rather than from confirmed failures, so a truck’s inclusion says only that it was built to haul liquid loads.
Sloshing liquid and the axle-load calculation
NHTSA lists the filing as campaign 26V620, with Mack’s own recall number SC0500, and describes the trouble as inaccurate axle load calculations that reduce braking performance when a truck hauls a smoothbore tanker trailer. Mack’s Part 573 safety recall report explains the mechanism: liquid movement inside a smoothbore or unbaffled tanker can introduce errors into the dynamic axle load figures the truck uses for trailer braking. The consequence, in the report’s words, is that “Loss of trailer brake effectiveness could result in extended stopping distance, increasing the risk of a crash or injury.”
A smoothbore tanker has no internal baffles, so the cargo can surge freely forward and back when the truck brakes. The report adds that “There are no warnings that precede this issue.”
Federal rules for air-braked trucks already set stopping limits, which gives the problem a yardstick. Under Federal Motor Vehicle Safety Standard 121, the table for loaded truck tractors allows 250 feet for the lighter categories and 310 feet for the heaviest ones, measured from 60 miles per hour. Those tests are run with an unbraked control trailer, so the figures describe the tractor itself and not a loaded tanker rolling behind it. The Mack recall concerns the second situation, in which the trailer’s own braking depends on a software estimate of how heavily each axle is loaded, and a sloshing cargo can skew that estimate.
Which Anthem and Pioneer tractors are covered
The Part 573 report splits the 850 trucks into two groups. The Anthem AN accounts for 544 vehicles built from July 8, 2025 through Sept. 21, 2026, and the Pioneer PR accounts for 306 built from Feb. 24, 2025 through Sept. 11, 2026. The affected component is a software package, part 26020191, supplied to the manufacturer by Bendix Commercial Vehicle Systems. Because the tanker application package is a selection criterion alongside model and year, trade reporting by Tank Transport notes that owners cannot rule a truck in or out from the badge alone and should check each vehicle identification number.
The same trade report adds a detail about geography. Dealer alerts dated Oct. 1 list 150 Mack vehicles in Canada, and the 850 figure covers the United States only, so the two numbers should not be added together or read as one tally.
The filing also lays out how the company reached its decision, and the timeline is short. Mack’s parent, Volvo Group, received a field report about a braking concern on a truck hauling smoothbore tankers on July 13, 2026, and a product safety alert followed the next day. Two more field reports arrived while engineers tried to reproduce the fault, a formal safety investigation opened on Aug. 26, an evaluation committee recommended escalation on Sept. 17, and the company’s safety committee decided on Sept. 21 that a safety issue exists and that a recall was warranted. The filing with NHTSA was received a week later.
Software that disables dynamic trailer braking
Dealers will install new software at no cost to owners. The update disables the dynamic trailer braking calculations, and Tank Transport reports that the change does not switch off the trailer brakes themselves. Operators who haul only baffled or compartmentalized tankers may keep their current software if they choose, and dealers can install the revised package later if one of those customers starts carrying smoothbore loads. A new sales code will mark trucks built to haul smoothbore or unbaffled tankers.
NHTSA’s record sets the schedule. Dealers were to be notified by Oct. 5, 2026, the same date the affected vehicle identification numbers became searchable, and owner notification letters are expected by Nov. 27, 2026 as the recall rolls out in phases. Owners can enter a 17-character number in NHTSA’s recall lookup or call Mack customer service at 1-800-866-1177 and cite recall number SC0500.
One question remains open in the public record. Tank Transport reports that the Oct. 1 dealer alerts said repair instructions would be released when available, and that the public documents do not establish whether the software was ready to install by Oct. 9. A tanker operator with an Anthem or Pioneer should therefore ask a Mack dealer for the campaign 26V620 remedy status before assuming the update can be installed on the first visit.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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