The Free Software Foundation tells us the scoop on this broadening scandal (emphasis mine):
Of course, just a few months after telling the Copyright Office that users couldn’t be trusted with access to their devices, the EPA revealed a major scandal involving Volkswagen. It turns out that Volkswagen had for many years cheated the emissions test performed by the EPA. Volkswagen had surreptitiously included some code in their diesel vehicles that would detect the EPA’s tests and have the car change its performance in order to meet EPA mandates. Once the test was over, the code would revert the vehicle to its normal, high-polluting functioning. This scam apparently went on for years before it was detected by researchers.
Of course the irony is that if users and researchers had the right to access the software on their cars, they might have discovered this fraud years ago. As Eben Moglen, founder of the Software Freedom Law Center noted “If Volkswagen knew that every customer who buys a vehicle would have a right to read the source code of all the software in the vehicle, they would never even consider the cheat, because the certainty of getting caught would terrify them.” Volkswagen is already a contributor on the kernel Linux, and as Bradley M. Kuhn, President and Distinguished Technologist of the Software Freedom Conservancy pointed out it is likely that Volkswagen vehicles already contain some free software. But some is not all, and clearly they kept much of their software secret in order to hide their scam. If all the software on the vehicles was free software they never could have perpetrated this scheme.