DETROIT -- Shares of General Motors fell about 2 percent Thursday afternoon after the company was accused in a federal lawsuit of cheating on government diesel emissions tests.
The lawsuit filed in U.S. District Court in Detroit alleges that GM pickup trucks with Duramax diesel engines have three devices on them that are rigged to allow more pollution on the road than during treadmill tests in the Environmental Protection Agency laboratory.
GM said the allegations are without merit.
The lawsuit filed by the Hagens Berman firm of Seattle alleges the trucks emit two to five times the legal limit for harmful nitrogen oxide.
Also named as a defendant is Robert Bosch LLC, which made GM's electronic diesel controls. Bosch says it is cooperating with government investigations into emissions cases and "defending its interests" in lawsuits.
Diesel engines have been under scrutiny worldwide since Volkswagen admitted its diesel cars cheated on tests.
The complaint against GM alleges the devices were installed on diesel engines in the Chevrolet Silverado and GMC Sierra heavy-duty pickups.
Two of the devices reduce emissions controls when the air temperature is above or below the range in government lab tests. The other reduces the level of emissions controls when the trucks are running continuously for 200 to 500 seconds. Government tests don't last that long, the lawsuit says.
The law firm estimates there are 705,000 of the diesel pickup trucks on U.S. roads.
The lawsuit demands a jury trial and seeks punitive damages, restitution and recovery of the purchase price of the trucks or the decrease in their values because of the devices.
GM called the claims "baseless" and said in a statement it would vigorously defend itself.
"The Duramax Diesel Chevrolet Silverado and GMC Sierra comply with all U.S. EPA and CARB (California Air Resources Board) emissions regulations."
A message was left Thursday for an EPA spokeswoman seeking comment on whether the agency is investigating the allegations.
The lawsuit comes just two days after the U.S. Justice Department sued Fiat Chrysler on behalf of the EPA alleging that some of its Ram diesel pickup trucks cheat on pollution tests. Fiat Chrysler has denied any wrongdoing.