I've discovered the Clarity PHEV does have an equivalent to the Volt's Engine Maintenance Mode so it will take care of itself when you're not using the ICE. You'll hear the ICE running but the car will show it's still in EV mode.
Yes but my point is we have no idea how often System Check runs. I have never experienced it even though since March I have twice gone more than a month without using ICE. And there was no highway or freeway driving during that time, only surface streets, so it is unlikely that ICE would come on without me hearing it. When ICE finally did come on it was because in both cases I accelerated into the gray area on the power meter. My experience of going over a month seems pretty common.
At least one person has reported that their car sat parked for over a month, and they fully expected ICE to run the next time they drove it, but it didn't, and didn't for several days and if I remember correctly they finally just ran HV because they felt that was too long for the engine to not run.
Pinning down the frequency of "true" System Check among Clarity owners is nearly impossible because in my opinion based on reading people's accounts they are often attributing normal startup events to System Check, like people who are not aware of the full battery regen ICE startup, they don't associate the ICE startup with using regen on a full battery (who in their right mind would?) and so they attribute it as a random ICE startup. And I really believe many people momentary accelerate just a smidgen into the gray area for a second without realizing it, but when you just barely go over like that even though ICE starts it seems to just idle and you can barely hear it until you stop at a light or whatever, causing people to think it was a completely random ICE startup.
I wish it told you in the maintenance screen, engine will start in (x) number of days if not used. Since it doesn't we are left to just guessing about it