They don't use the same supplier for all models. Sometimes the diesel variant can have a different supplier for the ECU (Engine Control Unit) than the gasoline

They don't use the same supplier for all models. Sometimes the diesel variant can have a different supplier for the ECU (Engine Control Unit) than the gasoline variant of the same model. They don't trust the entire production on a single supplier (strategic reasons). Bugs like this one can be noticed a bit late during production phase, so they will not be fixed, as they are not considered SoP (start of production) blockers. A new SW release costs a lot of money and they are requested on a need to have basis. The SW in the ECU is pretty big for an embedded device with just ~2MB dedicated to program flash: 500k-1m lines of code. And that is only for the engine. In a regular car maybe you have 10-30 on board computers. There are many more bugs in there, you just don't see them all. :-) (I'm working in the industry for such supplier)