A federal judge on Monday approved an estimated $85 million class-action settlement of a suit in which trucking customers alleged Pilot Flying J, the largest truck-stop chain in North America, defrauded them over several years through a diesel-rebate program.

The settlement, which is between Pilot and plaintiffs in 10 of about 20 pending lawsuits against it, requires the company to have auditors examine its trucking accounts and pay any money owed, in addition to 6% in annualized interest. It also assigns Pilot all legal and...