Not a mechanic nor a engineer here so my advice; take with a huge truck load of salt.
A) do you have sufficient coolant after you get the warning. If not, maybe a pinhole leak somewhere
B) It may be as simple as you need to burp the radiator, cause you may have air in your system. Their is a published DIY on how to bleed air from the system on either xoutpost or on here. Search is your friend.
Couple of options WHO KNOWS!.
Hope you get it fixed asap!
BMW and Mercedes Build Beta Products!
Lexus build Release Candidate Products!
Why does this matter?
CAUSE EVERY TIME someone says Lexus has better build quality, one should consider what Toyota their Lexus Engine and chassis platform comes out of and how long that part has been tested in the real world!