After checking the code for the failure for the SES/MIL lamp being on (you can turn the key from off to on three times, and the odometer will display the code which you can later look up in Google), I find that it was a cooler fan circuit failure. After washing the vehicle, the lamp goes out.

This wasn't just an odd occurrence, as this same solution has been used multiple times. I suspect water intruding into the harness to be suspect.