'02 UL w/ 125k. Riding down the street when the a Hi Height warning (red triangle) came on and stayed on despite stopping and restarting. I have never touched the switch. It doesn't seem to hurt anything and I wonder if it is a bad sensor, etc? On the other hand, could it be a warning that my air suspension is going? Any thoughts or ideas are appreciated, thanks.

 

The attached chart is for a 2004 LS430, but should apply to earlier model. According to this chart, there are a number of issues that can cause the "Height Hi" warning, each will throw a diagnostic trouble code (DTC). Please check to see which DTC you have.
In particular, take a look in the far-right column for anything with (O).