2005 STS. I'll be driving down the road and this message pops up and goes away, quite often. Like every few minutes. I've tried opening and closing the hood, to no avail. Seems like its closed. Where's the switch that tells the computer the hoods open? Not painfully evident. Car is new to me.

 

The 'Hood Ajar' switch is riveted to the hood latch assembly.

 

I found it on the back of the latch. Thanks Eric! I hosed it down with electronic contact cleaner, and so far so good.