flashing overdrive lights usually indicate an internal problem with the tranny.... for that, there will be a diagnostic code... i dont know the procedure on it, for toyotas, but when i had a flashing overdrive light in my ford, i hooked it up to a scanner, and one of my shift solenoids was bad... i replaced it by dropping the pan and this special cip thing, and when i reset the light, it never returned again....
