That's not really anything like dieselgate. Washing machines, I would hope, aren't emitting toxic gases that kill people.
It is, perhaps, a little deceptive if people believe their machines are more efficient than they really are on the commonly used cycles.
The way to solve this would be to improve the efficiency tests so that they test the efficiency of a fast cycle as well as an economy/long cycle.
Slow wash cycles are more efficient. Loosening the dirt by soaking means that less agitation is required. Manufacturers cheat the mandatory efficiency tests by making the default cycle very slow, but offering faster cycle settings. My washing machine takes nearly four hours for a standard cotton cycle, but has a "speed perfect" button that reduces the wash time to under an hour. I always use the fast setting.