It would be unlikely (not impossible) that board members would be briefed about ongoing criminal behaviour, and certainly not something so deep into operations as how the ECU is being programmed.

Can a board member be reasonably responsible for the actions of tens of thousands of employees if they have not explicitly enabled or condoned criminal behaviour?

The person that would benefit the most would be a senior executive who stands to gain a promotion, bonus or land an even better job elsewhere.

A former prime minister of my country was fined over $6 million for being on the board of a company what traded while insolvent. Not a prison sentence but a harsh penalty for someone that was not super rich (as far as I am aware).