I am trying to find the cause and hopefully a simple solution to the following problem. (This is a description of action and following effect.)
Start engine with transmission in P
Shift into D4: green "S" light comes on. At this point the "S" light is on o only in the D4 position of the shifter.
The transmission seems to be stuck in the "Sport shift" o mode; shifts at about 2500 rpm under normal load.
After a few minutes of driving (about 5-10 minutes) "S" light starts flashing and continues to flash in all positions of the shifter.
The speedometer does not work (show any speed indication).
When the engine is shut off and restarted the whole process starts over.

 

Looks to me like your vehicle speed sensor (VSS). It is rather easy to change out. Does your speedo jump around at all- or just not work? Either way, it is probably that. Have you checked the engine codes?

 

The speedometer does not work at all. No, I have not checked the codes because I do not have the equipment to do that. Since I got the same message from my guy at the Honda dealer I will assume that this is the correct diagnosis. This appears to be rather easy to change so I have purchased a new VSS and plan to replace it tomorrow (Thursday). Thanks for your help. I will post the results of this repair.

 

It is easy to extract the codes on a '91. You will have a two pin connector under the dash on the passenger side just above the kick panel. You can short out that connector with a paper clip and turn the ignition to on (not run). Then the computer will flash the codes to you. Short duration flashes are a single digit code; long are a second digit. I.E., three quick flashes is a code 3, Two long flashes and 1 short would be a 21. Multiple codes are separated by a long pause in between. You can do a search on google for engine codes and get all the code info..

 

I think that I have located the VSS on the transmission. This is located on top of the transmission on the firewall side. It is also buried under a bunch of hoses. It appears that I need to remove these hoses to get to the VSS. (which looks like a very tedious task) Is this right? I have not been able to locate the connector for the trouble codes despite many contorted positions. I will continue to look for it.