An interesting fact about Yaris which, I believe, majority people (including owners) don't know about & that is, how does Yaris Hill-Start Assist Control (HAC) works?
In our PKDM Yaris, it works by firmly pressing the break pedal (and then releasing break pedal) and it'll hold the breaks for couple of seconds. I've tested it today and it worked like a charm. FYI - after a couple of seconds or so, it'll release the break automatically. This is enough time to press accelerator & get going.
Being the owner of the Yaris Ativ MT & have a friend who owns 1.3 Ativ CVTi, I've tested it on both cars today.
The good thing is, this feature is completely automatic - no need to enable/disable this feature. Here's a good watch if you're interested to know about it.