On Monday, the US Department of Justice (DOJ) announced a settlement with an after-market car technology company called Derive Systems. Derive was accused of selling 363,000 devices that could defeat the emissions control systems of any car. The settlement called for Derive to spend around $6 million correcting its sold and unsold software to prevent further emissions tampering, as well as pay a fine of $300,000.

(Update, 15:10 ET: Derive added that all of its current products comply with EPA standards and "the removal of user-adjustable options do not depend on hardware fixes," so the company doesn't need to issue a formal recall.)

Derive's products rely on the OBD (On Board Diagnostics) II port that's found in most cars. Ars wrote about the company last year , noting that it is able to not only read diagnostics through the OBD II port, but to write via OBD II as well. This allows the company to re-map engine performance according to a customer's needs or wishes. If you own a fleet of delivery vehicles and you need to maximize efficiency (and minimize fuel cost) at the expense of, say, towing power, Derive's system would allow you to do that.

Unfortunately, it seems the company's software also allowed customers to re-map their engines in the opposite direction, favoring performance over emissions controls, which is verboten by the Environmental Protection Agency (EPA) and the Clean Air Act.

"Over a span of multiple years, Derive sold products, including custom engine tuning software and parts, online and at distributers across the nation under the brand names of 'Bully Dog' and 'SCT' for use in many types of gasoline and diesel-fueled cars and trucks," a press release from the DOJ noted. The DOJ refers to Derive's offending products as "defeat devices," a term that anyone familiar with Volkswagen Group's 2015 diesel scandal will recall. In regulatory parlance, a "defeat device" is any physical or digital addition to a car that "defeats" its emissions control system.

Back in the 1970's, defeat devices were actual switches that could, for example, sense very low temperatures and cut out the car's exhaust recirculation system to maintain good performance. These days, defeat devices are almost entirely software-based and usually quite difficult to spot.

The terms of the settlement between the DOJ and Derive are squarely focused on emissions-control-limiting functions; other types of tuning are still permitted. But some of the company's software will now come with more limits, and installation will require "a customer verification program for users of the custom tuning software, which includes training about vehicle functions, emission controls, and the Clean Air Act requirements," the DOJ wrote.

A lot of Derive's products are safety-focused and may not be affected. One function allows a customer to place geofencing restrictions on older cars so seniors with memory problems can't drive beyond a defined area. Another function prevents a car from starting unless seatbelts of all passengers are fastened. The settlement will only affect its performance-focused software.

The department added that "Derive must stop any marketing that would provide information on how consumers can defeat emission controls in their vehicles," as well. The DOJ added that Derive's relatively low fine of just $300,000 was "based on the company’s demonstrated limited ability to pay a larger amount."

Update, 15:10 pm ET: In a statement, Derive told Ars, "This is a very positive agreement for our business. With this agreement in place, we are the only federally compliant player in the automotive aftermarket industry. Every company in the aftermarket will now be held to the same standards."

The company added, "Under the agreement, we will make investments to demonstrate environmental leadership in the automotive aftermarket industry. These include: emissions tests on new and past model-year applications, developing additional training and certification for our custom tuning dealers, removing user-adjustable options associated with O2 [oxygen sensors] and EGR [exhaust gas recirculation], and building our compliance team."

"Every product we sell today is legal. We are permitted to and will continue selling our existing tuners and Advantage software," Derive said.

Update 17:45 ET: Derive noted that the $6 million figure was calculated in "negotiations with EPA as what we estimate the settlement will cost to implement, including training, certification, and testing." Derive noted that the estimate did not constitute a penalty or a fee.