In mid-September, the US Environmental Protection Agency dropped a bomb on Volkswagen Group, the German company that owns Volkswagen, Audi, Porsche, Lamborghini, and other notable car brands. The EPA sent the umbrella company a Notice of Violation, explaining that it discovered “defeat devices” on Volkswagen and Audi diesel passenger cars from 2009 and later.

The defeat devices—actually less a “device” than code on the cars’ electronic control module that detects whether a car is in a lab or on the road—were preventing the cars’ emissions control systems from working properly while the car was operating under normal driving conditions, likely boosting the car’s performance or fuel efficiency rating or both. The EPA said that nearly 500,000 of these diesel cars were caught spewing emissions well in excess of the federal rules, sending the company’s stock into a tailspin.

Just a few days later, Volkswagen announced that 11 million vehicles worldwide were outfitted with the emissions-boosting code, although not all of the cars had the dubious “feature” enabled, according to the company. Still, that sent Volkswagen’s stock into even more of a tailspin, and the company’s CEO was ousted within days. Multiple countries are now investigating Volkswagen for fraud, although in the US, Volkswagen might escape a criminal charge for violating the Clean Air Act (CAA), due to loopholes built into the Act by auto-industry lobbyists, The Wall Street Journal reports.

But for all this scandal in headlines, the whole debacle is not the first, or even the second, or even the third time the EPA has discovered automakers skirting emissions standards. And the EPA's rules and testing procedures are complicated enough that automakers have argued in the past that their defeat devices were legal because they solved performance problems on a car model while allowing it to pass the federally mandated tests. Often, car makers accused of defeating emissions control systems reach a settlement with the EPA or the Justice Department, but never admit guilt.

Because defeat devices have such a complicated history, it’s helpful to take a look at what a defeat device is, how the EPA tests for them, and what’s happened when they’ve been found in the past, to get some context for Volkswagen’s most egregious breach of public trust.

Hit the rulebook

The US Code of Federal Regulations (40 CFR 86.1803.-01), defines a defeat device as an "auxiliary emission control device (AECD) that reduces the effectiveness of the emission control system under conditions which may reasonably be expected to be encountered in normal vehicle operation and use.”

But the rules don’t ban defeat devices wholesale. The EPA can approve auxiliary devices to hinder the emissions control system on a vehicle—but the Agency has to know about it. Defeat devices can be allowed on emergency vehicles, for example. In a 2014 EPA document (PDF), the Southern Group of State Foresters reasoned that vehicle performance should always be prioritized over emissions control in emergency situations:

Numerous injuries and fatalities of wildland firefighters have occurred when dozers became disabled due to terrain such as becoming stuck or various mechanical reasons, while constructing firebreaks in front of advancing wildfires. It would obviously be extremely dangerous to have dozers with emission control systems or settings that could lead to dozers losing power, speed, or torque while constructing firebreaks in advance of an oncoming wildfire.

The tests

But passenger cars and commercial vehicles rarely need emergency torque. And so, automakers are required to complete a number of tests in a lab on a representative engine and submit those results to the EPA in order to show that the car they’re about to sell in the upcoming year is compliant with federal emissions standards.

The EPA can randomly check automakers' testing procedures, a practice called confirmatory testing. Notably, if a manufacturer is selected for confirmatory testing, the manufacturer provides the test engine or vehicle, and if it fails to pass the first test, the manufacturer can modify the engine (PDF) before a second round of confirmatory testing.

But setting aside confirmatory testing, standard testing procedures are different in specifics for heavy-duty vehicles (tractors, pickup trucks) and light-duty vehicles (passenger cars). For passenger cars, automakers must pass a Federal Test Procedure, or FTP, as well as Supplemental Federal Test Procedures (SFTP).

The current primary test procedure for emissions is called FTP-75. The car’s engine is hooked up to a dynamometer and run for about 31 minutes, testing it from a cold start, in a stabilized phase, and then with a hot start. "Emissions from each phase are collected in a separate teflon bag, analyzed and expressed in g/mile (g/km),” DieselNet explains. The car has to "travel" for 11.04 miles at an average speed of 21.2mph, with a maximum speed of 56.7mph.

Then, the car has to complete SFTPs to account for “aggressive, high-speed driving” as well as driving with the air conditioning on.

Gary Bishop, a research associate at the University of Denver who has worked on building systems to remotely monitor vehicle emissions in the real world, told Ars that the EPA’s tests set the manufacturers up for success, even if it’s not entirely warranted. “If anyone (including car manufacturers) knows the test ahead of time, why would anyone ever expect you to flunk that test?”

"One thing most people are not aware of is that manufacturers will have specific drivers who drive certain models because they can legally drive the test and produce the lowest emissions for that model,” Bishop continued. “[It’s] not cheating but one [can] expect that vehicle to behave differently off the test with real drivers.”

Bishop’s research partner, University of Denver Professor Donald Stedman, added that achieving a compliant but market-viable vehicle is often a difficult compromise. “Drivers want optimum power, performance and fuel economy, the EPA wants passing the test,” Stedman wrote to Ars. "This is why all auto companies hire very smart engineers, because these goals are often not compatible.”

A short and incomplete history of the defeat device

The past 50 years have shown that when those very smart engineers can’t quite make the EPA’s increasingly rigorous goals compatible, automakers will fall back on the fact that they only have to pass the EPA’s test—they don’t have to create a perfect car. That’s where defeat devices come back into play.

Volkswagen (the first time!) and others

The Clean Air Act (CAA) that regulates car emissions today was passed in 1963 and was revised a few years later to require stricter emissions standards on cars. Car makers, unsurprisingly, balked, and fought the EPA to extend the deadline for meeting the new standards.

Right about that time is when the EPA discovered the first analog defeat devices, with Volkswagen, oddly enough, being named one of the first violators of standards using the devices.

In a January 1974 Report to Congress (PDF), the EPA wrote that in the previous year it had opened an investigation concerning "the failure to report the existence of and the use of possible defeat devices by Volkswagen on a substantial number of 1973 model year vehicles" (page 43).

In an EPA press release from July 1973 (PDF), the administration noted that Volkswagen sold around 25,000 cars with temperature-sensing switches that were used to deactivate the emissions control system. Specifically, Volkswagen’s Fastback and Squareback 1973 models would sense low temperatures and cut out the cars’ exhaust recirculation system. In addition, 1973 VW buses had switches that would override “the transmission controlled spark-advance system at low temperatures.”

A year later Volkswagen, based in what was then West Germany, agreed to pay $120,000 (PDF) to settle the charges but did not admit any wrongdoing.

Around the same time, the EPA also reprimanded six manufacturers—GM, Ford, Chrysler, American Motors, Nissan, and Toyota—for installing devices which would "defeat the effectiveness of emission control systems under conditions not experienced during EPA’s certification testing.” The EPA ordered those devices to be removed from cars that were still to be produced, but it didn't order the recall of cars with devices that had already come off the assembly line. While the defeat devices apparently took different forms, The Sarasota Herald reported in late 1972 that the defeat devices found in the cars also activated in cold weather "in order to make the car start more easily." Alternatively, some models were equipped with time-delay switches that cut the emissions control system as an automatic transmission shifted from low to high gears.