Big Rigs · Nationwide · October 24, 2026

MX-13 Class Action Against Paccar Is Cleared to Head Toward Trial

A Washington judge has cleared the way for a class action against Paccar over EPA 2021 model year MX-13 engines to proceed to trial, Overdrive reports.

These are allegations in a lawsuit. No court has ruled on whether the engines were defective, and the trial is set for October 2027.

What the lawsuit alleges

According to Overdrive, 31 customers who say they bought Kenworth or Peterbilt trucks with the EPA 2021 MX-13 diesel engine filed an amended claim earlier this year. The case began in December 2023.

The plaintiffs allege the trucks had defective fuel systems that led to repeated breakdowns and months of downtime. The suit also alleges that Paccar knew or should have known about the problems and did not tell customers, and that it kept installing the engines without a permanent fix.

"Multiple class members have been driven to financial ruin by this issue and the resale value of affected trucks has diminished dramatically," the amended complaint says, as quoted by Overdrive.

The complaint alleges some customers reported a 60% drop in value based on buyback offers from the dealers who sold them the trucks new.

The suit says technicians pointed to failing fuel injectors, while Paccar looked into fuel additives and environmental factors. The complaint cites a statement from a Paccar executive who dismissed the idea that "bad fuel" was to blame, according to Overdrive.

What the plaintiffs want

According to Overdrive, the suit asks the court to order Paccar to notify class members of the defect, award damages, and pay for future fuel injector repairs until the design is proven to be a permanent fix.

Paccar's response

In its rebuttal, Paccar argued that the Clean Air Act, which covers the fuel system as part of emissions control, preempts the warranty claims, and that by replacing injectors at no cost it honored its warranty, Overdrive reports.

Judge Robert S. Lasnik rejected that argument. "Plaintiffs plausibly plead an engine warranty theory based on defects affecting the operation of the engine without regard to whether those same defects also affected emissions compliance," he said.

That ruling allows the case to continue. It is not a finding that the claims are true.

How many trucks

According to RigDig, as cited by Overdrive, about 14,000 active trucks have an MX-13 engine from model years 2021 to 2023, when Paccar used the EPA 2021 hardware.

A question for readers

Thirty-one owners say their engines kept breaking down. Paccar disputes the claims, and a trial is a year away.

Have you run an EPA 2021 MX-13, and how has it treated you?

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