There is no engineering error. And you are mixing Neutral and Park as one. It can charge just fine in Park. Neutral is where is cannot charge. Neutral has to be there, by basic safety requirements and by federal regulation, and the basic mechanics of the HSD mean that MG1 and MG2 cannot do any charging in this mode. To do such charging, Toyota would have needed to add a third generator directly on the engine shaft. That adds significant expense for a fairly case that can be reasonably addressed otherwise.
You still do not need to worry about it. It is nothing. Just turn off all battery draining stuff, then put it in neutral and go on through the car wash. I have been doing it for YEARS and nary a problem.
I know it can charge in park, I still find it kind of odd that then engine running in park can charge the battery but not in neutral. I'm trying to apply my limited understanding of engines to a Hybrid system, I must be missing something.... Since gas cars the engine runs and powers the alternator in neutral. Thanks for the attempted explanation, but I have no idea MG1 and MG2 even mean, lol. Edit: I read a bit more about stuff and figured out what MG1 and 2 are and I think I have an idea why it doesn't work now. I am not worried, more just curious. I usually run through the carwash with the AC blasting and music blaring and had never experienced this. I actually had the AC off when it happened though.
