Transmission on 1991 Acura Legend

D4 light flashs and speedometer falls to zero miles per hour
than back up to speed.

Asked by for the 1991 Acura Legend
The D$ light flashing indicates an automatic transmission fault but yo are lucky in that the Vehicle Speed Sensor (VSS) is a key sensor input for transmission controls. It operates the speedometer and is necessary fro cruise control as well. Common failure relatively easy to change and relatively inexpensive part (compared to a transmission failure).
my car is doing the samething the D4 light is flashing and speedo problems and from reading all the information I think its the VSS, my question is can I do it myself and what else should be done at the same time. Thank you.
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my legend unless up to high speed will not switch gears ....also will not go into gear unless in neutral first