SALT LAKE CITY — The Diesel Brothers have lost a bid for a court-mediated settlement conference they hoped could soften the blow of impending Clean Air Act monetary penalties.

Three stars of the Discovery Channel reality TV show and four corporate entities owned by one of them, David “Heavy D” Sparks, have been found liable for pollution violations and a judge is considering potential penalties of hundreds of thousands of dollars.

Attorneys for the Diesel Brothers on Jan. 15 asked U.S. District Judge Robert Shelby to order a new settlement conference, over the objections of the plaintiffs, Utah Physicians for a Healthy Environment.

The case has been trending against the Diesel Brothers, and unless the parties reach a settlement, the next step will be the issuance of findings of fact and conclusions of law by Shelby.

Janet Conway, representing the Diesel Brothers, said in the request for a conference that her clients “believe there is a strong likelihood the parties can settle, and are highly motivated to participate earnestly in a settlement conference.”

She said if the case cannot be settled, the Diesel Brothers “will certainly appeal,” which would add time and expense to the now 3-year-old case.

But in a following order, Shelby said he would not require a new settlement conference if the doctors’ group was not willing.

Earlier in January, the two sides filed documents with Shelby suggesting the levels of penalties the court should impose for the Diesel Brothers’ rigging of diesel pickup trucks to defeat federal emissions controls.

He said at that point he intended to give the two sides at least another two weeks before he issued final rulings “so that you all have a chance to think and press pause and meditate” and reach a “joint settlement” without court direction.

“The court accordingly declines to order a post-trial settlement conference over the objection of plaintiff,” Shelby wrote.

The judge gave no updated time frame for when his final rulings might be issued.

In its request for penalties, the doctors group said the Diesel Brothers should be ordered to pay $1 million, an amount that doctors’ attorney Reed Zars said would be sufficient to recover funds representing the economic benefits the truck builders have realized from rigging trucks.

In detailing potential penalties for all violations involved in selling 20 or more modified trucks and also selling “defeat parts” to consumers online, Zars contended that the law could justify about $4.4 million in penalties.

The Diesel Brothers argued that violations warrant $581,000 in penalties at most. More would drive Sparks Motors, the Woods Cross dealership where the trucks are built, into bankruptcy, they contended.

The doctors group sued in 2017 after its members noticed Diesel Brothers heavily promoting smoke-spewing modified trucks on the TV show and in their online truck giveaway sweepstakes.

Defendants include Sparks, his dealership, the online site Diesel Power Gear, and two other entities, 4×4 Anything and B&W Auto. Other Diesel Brothers named are Joshua Stuart, “Redbeard,” and Keaton Hoskins, “The Muscle.”

In the civil court trial last November, Zars asserted the Diesel Brothers’ actions heavily contributed to pollution along the Wasatch Front, which has among the worst air quality in the nation.

Any penalties ordered by the court would be paid to the U.S. Treasury, although up to $100,000 could be earmarked for a program to mitigate diesel pollution along the Wasatch Front.

Efforts to contact Zars were not immediately successful Monday.