An international team of researchers has revealed the intricate computer coding that enabled Volkswagen to manipulate emission tests in both the U.S. and Europe for over six years. This deception, which preceded the Environmental Protection Agency’s (EPA) notice of Clean Air Act violations in 2015, was achieved through sophisticated software embedded within the car’s onboard computer system. A year-long investigation uncovered how this code allowed the vehicle to recognize when it was undergoing an emissions test, subsequently activating emission-reducing systems. Once the test concluded, these systems were promptly deactivated.
Outside of test conditions, when the emission control systems were dormant, these vehicles emitted nitrogen oxides (NOx) at levels up to 40 times higher than EPA regulations permitted. The findings of this research, spearheaded by Kirill Levchenko, a computer scientist from the University of California San Diego, were presented at the 38th IEEE Symposium on Security and Privacy in the San Francisco Bay Area in May 2017. Levchenko stated, “We were able to find the smoking gun. We found the system and how it was used,” highlighting the team’s success in pinpointing the exact mechanism of the deception.
The computer scientists involved in the investigation accessed copies of the Volkswagen onboard computer code from publicly available sources, including the company’s maintenance website and online forums frequented by automotive enthusiasts. This code was found to be implemented across a broad spectrum of Volkswagen models, such as the Jetta, Golf, and Passat, as well as Audi’s A and Q series vehicles. Levchenko emphasized the accessibility of the evidence, noting, “We found evidence of the fraud right there in public view,” underscoring the somewhat open secret nature of the code.
Standard emissions testing procedures involve placing vehicles on a dynamometer, a device that measures engine power output while simulating driving conditions. The vehicle follows a standardized speed profile designed to mimic real-world urban driving, complete with frequent stops. The standardized and publicly known nature of these tests created an opportunity for manufacturers to intentionally alter vehicle behavior specifically during the test cycle. The code discovered in Volkswagen vehicles was designed to detect various parameters indicative of an emissions test, including distance, speed, and even steering wheel position. Upon recognizing these conditions, the code instructed the onboard computer to engage emission-curbing mechanisms exclusively during the test.
Uncovering the Code: A Year-Long Investigation
The investigation began as a collaborative effort between computer scientists at Ruhr University, independent researcher Felix Domke, and Levchenko’s team, working alongside Professor Stefan Savage’s research group at the Jacobs School of Engineering at UC San Diego. Savage and Levchenko’s team brought to the project their extensive background in analyzing embedded systems and identifying vulnerabilities in automotive onboard computers, specifically Engine Control Units (ECUs). The team meticulously examined approximately 900 different versions of the software code and discovered that around 400 of these versions contained the deceptive coding designed to circumvent emissions tests.
A particular segment of the code was labeled “acoustic condition,” ostensibly intended to manage engine sound. However, this label served as a euphemism for the conditions encountered during an emissions test. The code was capable of recognizing up to ten distinct profiles associated with potential tests. When the computer determined that the vehicle was undergoing an emissions test based on these profiles, it activated the emission control systems, effectively reducing the amount of nitrogen oxide emitted to compliant levels. Levchenko described the sophistication of the system, stating, “The Volkswagen defeat device is arguably the most complex in automotive history.”
In contrast to Volkswagen’s complex system, researchers found a simpler circumvention strategy in the Fiat 500X. The Fiat’s onboard computer was programmed to simply run its emissions-curbing system for a fixed duration of 26 minutes and 40 seconds after the engine started – a period roughly equivalent to the length of many emissions tests. Interestingly, researchers pointed out a common link: Robert Bosch, a major automotive component manufacturer, produced the Engine Control Units for both Volkswagen and Fiat vehicles. The car manufacturers then customized the code by inputting specific parameters to enable the deceptive functionality.
Diesel engines, in particular, present emission control challenges due to their combustion process generating higher levels of particulates and nitrogen oxides compared to gasoline engines. To meet emission standards, the onboard computer systems in diesel vehicles sometimes need to compromise performance or fuel efficiency in favor of emissions compliance. This study underscores the growing regulatory challenges in effectively verifying software-controlled systems that are designed to conceal their true operational behavior. It also highlights the need for developing new verification techniques suitable for adversarial situations where systems are intentionally designed to deceive. Levchenko concluded, “Dynamometer testing is just not enough anymore,” emphasizing the inadequacy of current testing methods in the face of sophisticated software-based manipulations.
Publication Details
“How They Did It: An Analysis of Emission Defeat Devices in Modern Automobiles”
Authors: Guo Li, Kirill Levchenko, and Stefan Savage from UC San Diego; Moritz Contag, Andre Pawlowski, and Thorsten Holz from Ruhr University; and independent researcher Felix Domke.
This research was supported by the European Research Council and the U.S. National Science Foundation (NSF).
