Mack Trucks has told federal regulators that 850 of its newest heavy trucks carry brake-control software that miscalculates axle load when the truck is configured as a tanker. The campaign, numbered 26V620, covers 2026 and 2027 model-year Anthem and Pioneer tractors that were built with Mack’s tanker application package.
Braking is the function at stake: when the software gets the load wrong, the trucks need more room to stop.
The axle load calculation in the filing
NHTSA’s campaign record, with a report received date of September 28, 2026, lists 850 potentially affected vehicles under the component heading “service brakes, electric: software/programming.” Mack’s filing says the trucks, equipped with a tanker application package, run into “inaccurate axle load calculations” that compromise braking capability while hauling smoothbore tanker trailers. A smoothbore tank has no internal baffles, so liquid in it can surge forward and back when the truck brakes.
The consequence statement is plain. The defect can produce “reduced braking performance” that “can require a greater distance to stop, increasing the risk of a crash.”
Anthem and Pioneer models in the recall
The recall names the 2026 to 2027 Anthem AN (4) and the 2026 to 2027 Pioneer PR (4). The population is not every Anthem or Pioneer built in those years, only those with the tanker package, and at 850 it is far smaller than the 2,772 trucks in an earlier Mack campaign on the same nameplates. Mack’s own description of the Anthem calls it a Class 8 heavy-duty truck offered in day cab and sleeper versions, with 4×2 through 8×6 axle layouts and engines rated from 345 to 505 horsepower, so the tanker package is one of many ways the truck leaves the factory.
The earlier Mack campaigns on these lines were hardware problems. Recall 26V261, received April 23, covered 2,772 units and involved rear brake modulators whose unprotected electrical connectors could short circuit and disable anti-lock braking and electronic stability control. Recall 26V351, received May 28, covered 644 vehicles across the Granite, Anthem, Pinnacle and Pioneer lines for wheel lug nuts that could loosen and let a wheel detach. The 26V620 defect differs in kind: it sits in the code that decides how hard the brakes can work, not in a part that can short or loosen.
The software remedy and the notification dates
Dealers will install a software update at no charge that, in Mack’s words, will “disable the dynamic trailer braking calculations.” The recall text does not explain what the truck falls back on once those calculations are switched off, and it does not describe any change to the hardware. The earlier 26V261 fix was physical by comparison: dealers inspect rear brake modulator connectors, install protective covers and replace modulators as needed.
The schedule is staggered. VIN search on NHTSA’s site begins October 5, 2026, and owner notification letters are scheduled for November 27, which leaves a gap of 60 days between the report to NHTSA and the mailing. Mack’s internal designation for the campaign is SC0500. Fleet operators with a tanker-package Anthem or Pioneer can enter a 17-character VIN at NHTSA’s recall lookup once it opens to see whether a particular truck is among the 850.
NHTSA’s count is a potential-units figure, meaning the trucks that could carry the condition rather than trucks confirmed to have it. At 850 it is about 31 percent of the 2,772 units in the April rear brake modulator campaign, and it comes in the third Mack campaign of the year on these nameplates, after reports on April 23 and May 28. Two of the three involve braking, one in hardware and one in software.
Tanker loads and stopping distance
Liquid cargo makes load estimation harder, because a tanker’s weight changes with its fill level from one trip to the next. The filing ties the miscalculation to the tanker application package, so the 850 are the trucks built with that package. The record does not say whether the software errs high or low, only that its axle load figures are inaccurate and that stopping distance can grow as a result.
The notification gap is longer here than in the April campaign. For 26V261, received April 23, Mack mailed owner letters on June 8, 46 days later. For 26V620, received September 28, the letters are scheduled for November 27, 60 days out, and the NHTSA record gives no interim instruction for tanker operators in the meantime.
Small figures frame the case: 850 trucks, a September 28 report, a November 27 mailing date. Of the three, the date NHTSA lists as the start of VIN search, October 5, is the first one an operator can act on, because it settles whether a given tractor is among the 850 or not.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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