To access the relay remove the glovebox. It is tucked around the left side of the opening in the dash. A white relay about 1" x 1" x 2 1/2". Trust me it is there, but if it has not been removed before might be hard to locate.

Remove the relay and open it up. With a strong light and a magnifying glass look for a bad solder joint on the circuit board. Sometimes they are easy to see other times not....

You can resolder the defective joint if you find one or better yet is to reflow all the joints on the board.

You should hear/feel the relay click each time you press the button on the shifter. It is much easier to find out if that is happening with the relay in your hand.

Most often overdrive problems are found to be based in the relay and going there first narrows the chase. Wiring from the switch to the relay or relay to the solenoid is suspect as well, but starting with a healthy relay is usually best.

Randy