A year of digging through code yields “smoking gun” on VW, Fiat diesel cheats

Current US and EU emissions testing is insufficient to confirm compliance.

Auto manufacturers have been cheating on emissions control tests for decades, but until recently, their cheats were fairly simple. Temperature-sensing or time-delay switches could cut the emissions control system when a car was being driven under certain conditions.

.. The researchers found that the cars assumed they were being tested in a lab until a sensor reading ruled out a lab test. At that point, “the vehicle can switch to an operating regime favored by the manufacturer for real driving rather than the clean regime necessary to pass the emission test,” the research paper noted (PDF).
Earlier, more basic versions of the software checked for three conditions to decide whether a lab test was being conducted. But by 2009, some firmware versions included 10 different checks for a lab test. The cars checked for things like how long and how far the car had been driven (in the US, emissions cycle tests last no more than 31 minutes and the car drives exactly 11.04 miles). Some cars also may have conducted steering wheel checks—if the steering wheel deviated more than 20° from neutral position, it was probably not being tested in the lab.
.. In many of the function sheets, the code to cheat emissions tests was labeled as modifying the “acoustic condition” of the engine