VW emissions scandal: how Volkswagen's 'defeat device' works
Source : VW emissions scandal: how Volkswagen's 'defeat device' works
The vehicles affected by Volkswagen’s emissions scandal are capable of detecting when they’re being tested – here’s how the ‘defeat device’ can be able to cheat the test
The Environmental Protection Ageny’s (EPA) official notification issued to Volkswagen on 18 September sheds light on how Volkswagen managed to influence the emissions tests with some clever software.
“VW manufactured as well as installed software inside the electronic control module (ECM) of these vehicles that will sensed when the vehicle was being tested for compliance with EPA emission standards,” the agency explained.
The EPA refers to what This kind of calls a ‘switch’ that will enabled your vehicle’s ECM to know when This kind of can be being tested on a rolling road: “The ‘switch’ senses whether the vehicle can be being tested or not based on various inputs including the position of the steering wheel, vehicle speed, the duration of the engine’s operation as well as barometric pressure. These inputs precisely track the parameters of the federal test procedure used for emission testing for EPA certification purposes.
“During emission testing, the vehicles’ ECM ran software which produced compliant emission results under an ECM calibration that will VW referred to as the ‘dyno calibration’.
“At all different times during normal vehicle operation, the ‘switch’ was activated as well as the vehicle ECM software ran a separate ‘road calibration’ which reduced the effectiveness of the emission control system. As a result, emissions of NOx increased by a factor of 10 to 40 times above the EPA compliant levels, depending on the type of drive cycle (e.g. city, highway).”
All US vehicles must be issued which has a certificate of conformity that will proves they adhere to environmental standards.
To obtain a certificate of conformity, a the must submit a list of all auxiliary emission control devices (AECDs) present on the vehicle. The EPA’s definition of an AECD can be “any element of design which senses temperature, vehicle speed, engine RPM, transmission gear, manifold vacuum or any different parameter for the purpose of activating, modulating, delaying or deactivating the operation of any part of the emission control system.”
The issue facing Volkswagen can be the switchable system inside the ECM was not declared.
“Due to the existence of the defeat devices in these vehicles, the affected Volkswagen vehicles do not conform in all material respects to the vehicle specifications described inside the applications for the certificates of conformity that will purportedly cover them,” said the EPA.
A defeat device can be an AECD “that will reduces the effectiveness of the emission control system under conditions which may reasonably be required to be encountered in normal vehicle operation as well as use. Motor vehicles equipped with defeat devices cannot be certified.”
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