The D4 light flashing means the transmission computer detected a problem and stored a code specific to that problem. You need to get that code and post it on here. Then we can give you more detailed instructions.
To get the code, get a thin paperclip or piece of wire and short a blue two-pin connector behind the passenger kick panel. Turn the key to the II position, and count the D4 light flashes. A long blink =10 and a short blink=1, so L SSS =13.
You might as well count the check engine light too if it starts flashing codes. That would tell you if the engine computer detected a problem.
See this site that has some pics. http://www.techautorepairs.com/dtc.html