The flashing OD light is sort of the equivalent of the check engine light for the transmission. When a transmission related code is set, the light will flash.
All this means is that some transmission related system being monitored has reported a result out of the expected for that system. In some cases it might be something serious - in which in a majority of cases will show up as a driveability concern. On those you should NOT continue to drive it much at all until you have it fixed.
Some codes may be relatively benign... in which case you could drive a while without any real worry.
Some might not show up in the apparent operation, but yet require more prompt attention.
How do you know which one it is? Bottom line - When you have a code set, it is a good idea to find out what it is.
If the concern that set the code did not reappear after a few "drive cycles" the light will stop flashing. The code will remain in memory, but since it is not a current concern, and nothing is being sensed out of the ordinary presently, everything is ok for the moment and you can continue to drive without worry - I note however that in the case of transmission codes, most of them that appear will reappear.
Hope this helps.