Fiat Chrysler Automobiles (FCA) and engine supplier Cummins are the latest companies to be accused of hiding excess diesel-exhaust emissions.

A class-action lawsuit filed against the two companies Monday accuses them of conspiring to conceal illegally-high levels of emissions in Dodge Ram 2500 and 3500 diesel pickup trucks manufactured between 2007 and 2012.

These trucks are heavy-duty models equipped with 6.7-liter Cummins engines, not to be confused with the light-duty Ram 1500 EcoDiesel, which was introduced in 2014 and uses a 3.0-liter engine from Fiat subsidiary VM Motori.

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The lawsuit alleges that FCA predecessor Chrysler Group LLC and Cummins hid the fact that emissions-control devices couldn't lower emissions to legal levels.

The Cummins engines involved in the suit primarily used two devices to lower nitrogen-oxide (NOx) emissions: a diesel-particulate filter and a NOx absorption catalyst system (NAC).

An NAC system's catalyst is supposed to absorb NOx and break it down into less-harmful substances, while particulate filters capture particulate matter that is a byproduct of combustion in diesel engines, and can be harmful to humans if inhaled.

2010 Dodge Ram 3500

2010 Dodge Ram 3500

The suit alleges that catalysts in the affected trucks were not robust enough to handle the emissions produced by the Cummins engines.

This meant that trucks produced emissions in excess of legal limits, according to the lawsuit.

In addition, the lawsuit claims injection of fuel to regenerate the particulate filter occurs with "excessive frequency," which could lead to higher fuel consumption and emissions.

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Faults with emission-control equipment have also caused exhaust-system components to prematurely wear out, requiring replacement at an average cost of $3,000 to $5,000, according to attorneys.

The suit was filed by Seattle law firm Hagens Berman Sobol Shapiro, which was involved with the Volkswagen 2.0-liter diesel settlement, and has also filed a suit against General Motors for alleged emissions cheating on Chevrolet Cruze Diesel models.

Attorneys seek reimbursement and damages for as many as 500,000 truck owners.

2010 Dodge Ram 2500

2010 Dodge Ram 2500

FCA said in a statement that it is reviewing the Dodge truck complaint, but does not believe it is meritorious, according to Bloomberg.

The automaker said it would contest the suit, and a Cummins spokesperson interviewed by Bloomberg said the supplier would do so as well.

Neither the U.S. Environmental Protection Agency (EPA) nor the Justice Department have taken any apparent action against FCA or Cummins on this matter.

The lawsuit alleges that the root of the two companies' emissions cheating was a set of stricter EPA standards issued in 2001, to apply to vehicles in model-year 2010 and later.

2010 Dodge Ram 3500 HD

2010 Dodge Ram 3500 HD

According to the suit, Chrysler and Cummins saw the tougher regulations as a "golden business opportunity" to get emission-compliant trucks on sale before their competitors.

Cummins also sought to bank emissions credits to compensate for other, dirtier engines, the suit alleges.

But engines could not be made to meet the stricter standards within the required timeframe, so a cheat was devised instead, according to the suit.


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