Volvo Repair: 4th gear disengagement, orange arrow, fuse panel

Question
I have a '93 240 with 117K miles. On a road trip driving back from Maine to Brooklyn this last week the orange arrow light went on indicating that the 4th gear had been disengaged (I was on the highway at 65 mph at the time). When I pressed the button on the left side of the gear shift it did not   
reengage the 4th gear and has not reengaged driving around town. I had this problem before and asked my mechanic, but he had no idea what to do about it. At the time 4th gear reengaged on its own while I accelerated. Do you know what I can do about this and if my engine will be damaged if I continue to drive it?

Thanks,
Daniel

Answer
it will make the engine run at higher rpm and use more gas and cause more wear than normal.I would get it fixed.more than likely the overdrive relay is bad.the overdrive  relay is located on the fuse panel behind the ashtray.remove the ashtray and then remove trim around lighter socket then you will see 2 screws remove the screws and the storage area will come out the relay is white and about 1x1x3  inch.it will be towards the passengers side of the panel.