Two auto manufacturers are in legal crosshairs this week because of emissions from their diesel vehicles.

The US Department of Justice sued Fiat Chrysler of America (FCA) on Tuesday over 103,828 diesel Ram 1500s and Jeep Grand Cherokees. The DOJ claims that the cars contain “at least eight software-based features” to meddle with the cars’ emissions control systems.

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And today, two plaintiffs have asked a judge to let them proceed with a class-action lawsuit against General Motors. They claim that 705,000 of the American carmaker’s diesel Silverado and Sierra HD trucks are giving off nitrogen oxide (NO) emissions in excess of what a consumer would expect and what the Environmental Protection Agency (EPA) legally allows.

The lawsuits represent more hurdles for diesel technology in light-duty vehicles. Emissions problems came to the fore with the Volkswagen Group scandal in 2015, which has led to some of the biggest fines from a regulator in automotive history. At issue is the nature of diesel engines, which tend to emit more NO x than gas engines.

In order to remove a substantial amount of NO x and other particulates from emissions, automakers have a number of options, many of which require tradeoffs that are more noticeable on light-duty vehicles than heavy-duty vehicles. In Volkswagen’s case, the company has admitted to cheating on federal emissions tests by installing hidden software that activated the emissions control system during lab conditions and reduced the system's effectiveness of those controls during real-world driving.

Rams and Jeeps

The EPA announced in January that it was investigating some irregularities with the emissions from diesel FCA vehicles. Although reports came out late last week that FCA would be issuing a minor software update to bring the cars in question into compliance, thereby potentially avoiding a lawsuit from the Justice Department, that scenario has not played out so favorably for the automaker.

The US government filed a complaint on Tuesday (PDF) claiming that FCA asked Bosch—the same German auto parts supplier that VW Group got its engine software from—to “customize” the engine control system software that FCA used in its diesels.

The complaint details how each of the eight so-called defeat devices found across the 103,828 vehicles in question worked. One program, found in 2014 diesel Ram 1500s and Jeep Grand Cherokees, completely turned off the Exhaust Gas Recirculation (EGR) system as soon as the car got up to highway speeds. Another, found on 2015 and 2016 Rams and Jeeps, reduced the effectiveness of the EGR system as speeds increased. (The US emissions test, which takes place in a lab, occurs at an average speed of 21.2 mph.) Another program disabled the Selective Catalytic Reduction (SCR) system, which sprays urea into exhaust to reduce NO x to nitrogen and water. Another delayed refilling the SCR catalyst with ammonia at certain intervals to keep the system working normally.

“The magnitude of the emissions increase depends on, among other things, the type of Subject Vehicle and the driving conditions,” the complaint notes.

In a statement, FCA contested the complaint:

The Company intends to defend itself vigorously, particularly against any claims that the Company engaged in any deliberate scheme to install defeat devices to cheat US emissions tests. As FCA US announced last week, it has developed updated emissions software calibrations that it believes address the concerns of EPA and CARB [California Air Resource Board].

GM pulled into the fray

The proposed class-action lawsuit against GM (PDF) claims that the company’s Silverado and Sierra 2500HD trucks with Duramax diesel engines rely on at least three different programs to reduce the effectiveness of the emissions control systems found on the cars. One program allegedly reduces the effectiveness of the emissions system when temperatures rise above 86 degrees Fahrenheit. A second program allegedly reduces effectiveness below temperatures of 68 degrees Fahrenheit, and a third “reduces the level of emissions controls after 200-500 seconds of steady speed operation in all temperature windows, causing emissions to increase on average of a factor of 4.5,” the complaint reads.

The plaintiffs add:

Based on a study of temperatures in 30 major metropolitan areas, as well as the demographics of Silverado sales, it is estimated that due to the temperature-triggered defeat devices, the vehicles operate at 65-70% of their miles driven with emissions that are 2.1 to 5.8 times the standard.

The complaint also claims that Bosch, again, was responsible for developing the electronic diesel control system that GM used in its trucks.

In response, GM seems to have taken a page from FCA's book. A statement from the company reads, “These claims are baseless, and we will vigorously defend ourselves. The Duramax Diesel Chevrolet Silverado and GMC Sierra comply with all US EPA and CARB emissions regulations."