punitive response from regulators
A bowed head isn't going to fix it. A fine isn't going to fix it either as fines are just considered a cost of business and will be passed onto consumers in one way or another. But what will change behaviour is penalising their future scores. Cheat by 10% and be penalised by 20%. Cheat with a million cars, have the 20% penalty against 2 million. 4 models caught, penalise 8. Done it for 2 years, penalise for 4.
At the end of the day, they are stealing customers off their competition, so this approach would give that competition a leg up and create a strong disincentive to cheat.