A class-action lawsuit accuses General Motors of rigging emission-control systems on 2011–2016 Chevrolet Silverado HD and GMC Sierra HD pickups with GM’s Duramax turbo-diesel 6.6-liter V-8 engine. If the allegations are proved true, the environmental damage from these 705,000 trucks, which the lawsuit said emit two to five times the legal limit of nitrogen oxides (NOx) in typical driving conditions, could easily exceed that of Volkswagen’s emission-test-cheating TDI engines.

The complaint, which was filed in U.S. District Court for the Eastern District of Michigan, cites tailpipe emissions for nitrogen oxides (NOx) with these turbo-diesel 6.6-liter V-8 engines that are well beyond the legal limits. The document also frequently mentions Volkswagen and suggests that, to be brought within compliance, these GM trucks are likely to need modifications that could hinder performance as well as fuel economy.

The suit claims that GM used at least three defeat-device tricks in these trucks. The automaker is alleged to have programmed the emissions software to relax or “derate” its emission controls after five to eight minutes of steady highway driving—a use case that isn’t part of an emission test cycle. Such behavior would also likely extend the interval for adding urea-based diesel emissions fluid (DEF), which serves to reduce NOx in the exhaust stream. With second and third defeat-device software hoops, GM also reduced emission controls below an ambient temperature of 68 degrees or above 86 degrees—the specified range in which the EPA emissions test cycle must be run.

It’s important to note that, so far, these are consumer statements. There’s not yet any accusation from regulators or any federal investigation announced by the U.S. Environmental Protection Agency (EPA) or the California Air Resources Board (CARB).



The suit names both GM and the German supplier Bosch, with Bosch called “an active and knowing participant in the scheme to evade U.S. emissions requirements.”

Cheating or Cleverness?



“A defeat device, as defined by the EPA, is any apparatus that unduly reduces the effectiveness of emissions control systems under conditions a vehicle may reasonably be expected to experience,” the complaint notes.

At the center of the continued woes for automakers and diesel-emission claims is a disconnect. While emission regulations might be based on legal limits, vehicle compliance is based around measurements during closely defined driving cycles. The EU is in the process of adopting new Real Driving Emission (RDE) test procedures that would help better align legal limits with tailpipe output. One study, published in Nature this month, said that NOx emissions of U.S. Tier 2 light-diesel vehicles—including but not limited to VW vehicles with defeat devices—are estimated to be about five times actual limits.

The firm that filed this suit on behalf of consumers, Hagens Berman, has a full roster of other current automotive-litigation cases, including active lawsuits regarding the Chevrolet Cruze diesel and the Dodge Ram 1500 EcoDiesel and Jeep Grand Cherokee. It’s also the firm behind the massive consumer settlement regarding Volkswagen, Audi, and Porsche diesels.

GM released a statement flatly denying the claims in the lawsuit, saying they “are baseless, and we will vigorously defend ourselves. The Duramax Diesel Chevrolet Silverado and GMC Sierra comply with all U.S. EPA and CARB emissions regulations.”



The GM case joins other allegations that have been active for some time, including an ongoing federal investigation of Mercedes-Benz diesels and FCA’s effort to make good with EPA and CARB and current status as the subject of a U.S. civil suit,

While the future and merit of accusations toward GM are uncertain at this point, it’s increasingly clear that the VW scandal has cast every automaker’s diesel engines in a new and unflattering light, and it’s equally clear that regulators and law firms now smell blood—or is that diesel fuel?—in the water.

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