Red Triangle Light when Weight in Backseat

Have had this issue for a while on my '07 Prius, probably a good 50k-70k miles and have never thought much about it. But since I'm back on here relearning about coolant issues for my '08 figure I'd get some opinions.

But whenever I have a passenger sit in the back seat, my little red triangle eventually pops up and sporadically goes on and off until I no longer have the passenger. I've gone through tire changes and such over this time so doubt it's tire pressure (if that would even spur the red triangle) if it would maybe it's a faulty sensor?

I also encounter a temporary red triangle when doing semi long turns when I exit the interstate, which might be related.

Any idears?