The VW scandal came to light when researchers from the International
Council on Clean Transportation and West Virginia University performed
all kinds of tests on VW vehicles, discovering that when the vehicles
were on the road, they polluted substantially more than when they were
being tested for pollution emissions.
If this software was open-source (not even free!) the process to find the problem woudl be much easier and less costly. And most probably the issue would not occur at the very first place - VW engineers woudl not have temptation to do what they did.
Do you think VW case can be used as an example of the benefits which free software might provide to the society?