Overdrive flashes on and off?

It sounds like it needs to be rebuilt. I would check the fluid level first and maybe service the transmission to see if that helps.

Here are a few guides to help us fix the problem:

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

and

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Also, we should run the codes because you might have a pressure regulating solenoid that is not working.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Check out the images (below). Please let us know how it goes