2011 Honda CR-V
The D3 light randomly illuminated. What does it mean and what did I do to cause this? (I was doing regular, local driving--nothing new or unusual.)
Thanks.
See if the below image below helps:

That would indicate your transmission is in direct drive. Usually this happens if you have inadvertently switched off the overdrive or have put the gear selector in the wrong position.
You can find the owners manual at the Honda Site.