Ever since news surfaced that VW had engaged in massive fraud and criminal misrepresentation of its TDI “Clean Diesel” products, there have been questions about how the company did what it did. It’s one thing to see the effects of the software code in action, and repeated real-world driving tests in a huge range of conditions across multiple vehicles confirmed the problem long ago — but that’s not the same as knowing where the code is or how it works.
According to the Jacobs School of Engineering at UC San Diego, the code in question was masquerading as if it was related to engine noise. In reality, it was watching for a specific set of conditions. The rules the EPA uses for evaluating vehicle mileage are a matter of public record, as are the test procedures. That’s arguably a good thing, as it tells consumers how products are evaluated and how the results are calculated. While most people just look at the final numbers, you can use information on how tests are performed to perform more precise calculations on which vehicle or vehicles might be right for your own use cases.
But making those rules public does have a downside: It means companies know precisely how to cheat. Here’s how the Jacobs School describes the situation:
During emissions standards tests, cars are placed on a chassis equipped with a dynamometer, which measures the power output of the engine. The vehicle follows a precisely defined speed profile that tries to mimic real driving on an urban route with frequent stops. The conditions of the test are both standardized and public. This essentially makes it possible for manufacturers to intentionally alter the behavior of their vehicles during the test cycle. The code found in Volkswagen vehicles checks for a number of conditions associated with a driving test, such as distance, speed and even the position of the wheel. If the conditions are met, the code directs the onboard computer to activate emissions curbing mechanism when those conditions were met.
But VW didn’t stop there. The researchers who examined Volkswagen’s work pulled 964 separate versions of the Engine Control Unit (ECU)’s code from various makes and models of Volkswagens. In 400 of those cases, the ECU was programmed with defeat devices.
Now, you might be thinking that a single code model couldn’t possibly compare all the variables in play between various test facilities, and that some cars should have shown a fault simply due to random chance. But VW was aware of that possibility and took steps to prevent it. Their defeat device had ten separate profiles to allow it to detect various permutations in test scenarios.
Not all the defeat devices were sophisticated. The Fiat 500X (not manufactured by VW) has a much simpler defeat device. The vehicle’s emission control system runs for 26 minutes and 40 seconds after you first start the car, period. That’s long enough to pass most emission tests, and it doesn’t try to detect if the vehicle is being tested. But VW’s work was extremely sophisticated, it evolved over time, and the company’s claims that this was all instituted by a few rogue engineers are more farcical than ever.
source : https://www.extremetech.com/extreme/249891-vws-diesel-defeat-devices-finally-located-cracked-wide-open