I have a 1995 Honda Accord which has been giving me some trouble lately. Recently, on occasion, the spedometer will begin move erratically and the d4 light will begin flashing. When I stop the car, turn it off, and restart it, the problem rectifies itself for a while. I pulled the transmission fault codes and got 4 (vehicle speed sensor) and 15 (main shaft speed sensor) I also received the VSS fault code from the ECU. Is this all related to the same problem or seperate issues.

 

Codes 9 and 15 are related to the two magnetic sensors located on the right side cover of the AT housing. Use a 10mm wrench and pull the two sensors, make sure they are clean of any junk, slurry, and that the wiring is good and the sensors resistance is within spec.
Scroll half way down this page to read up on the NM/NC sensors > http://techauto.awardspace.com/transmission.html

About directly underneath where the throttle body is, located in the differential housing is where the VSS is located. Sometimes the sensor can be pulled apart, cleaned, reinstalled and it works again. But it may need to be replaced.
http://techauto.awardspace.com/vss.html