This is actually a product design problem. In my best understanding (I am not a designer--someone please correct me if I'm wrong!), this is a failure with the Gulf of Evaluation:
https://en.wikipedia.org/wiki/Gulf_of_evaluation
Essentially, the entire system and its state should be immediately evident and intuitive to the person using the system. If a Deaf person doesn't get a visual signal that the engine is still running then they don't understand the engine is running, and thus this is a big Gulf of Evaluation issue.
