Seven years after the Volkswagen diesel scandal began, emissions "defeat devices" are still a problem, but now it's mostly aftermarket companies that are drawing the attention of regulators.

The EPA recently announced the levying of millions of dollars in fines against companies selling aftermarket solutions that go by a wide range of names, including tunes, tuners, or delete kits. The common thread is that they all have been selling equipment allegedly designed to circumvent pollution controls, which is illegal under the Clean Air Act.

2022 Ford Super Duty

2022 Ford Super Duty

Keystone Automotive, a parts distributor headquartered in Exeter, Pennsylvania, will pay $2.5 million in a settlement for selling these defeat devices. It's the third largest civil penalty settlement of its kind nationwide, the EPA said in a press release.

The company was cited for 15,621 violations, including selling 44 types of aftermarket parts that can defeat emissions controls for particulate matter and nitrogen oxides (NOx), potentially allowing vehicles to release larger amounts of both pollutants into the atmosphere, according to the EPA.

Shortly after that settlement was announced, the Justice Department filed a Clean Air Act complaint on behalf of the EPA against Peoria, Illinois, company RCD for "manufacturing, selling, and installing" defeat devices, and is seeking "monetary civil penalties and injunctive relief," according to a second EPA release.

2023 Chevrolet Silverado 2500HD

2023 Chevrolet Silverado 2500HD

A robust market for these defeat devices has existed for years. An EPA report issued in late 2020 called some of these companies out as big business, and threatened fines.

Tampering with emissions controls often goes hand in hand with increasing the performance of diesel trucks. These types of modified trucks were even spotlighted on the Discovery Channel show "Diesel Brothers," which profiled a Utah shop that built them but was later sued by local doctors for alleged illegal modifications.

Studies have shown that the increased NOx and particulates produced when emissions controls are disabled can have demonstrable health effects.