1981, stock with all CCC parts on and operational.

Once in a while I am getting a Code 24, Vehicle Speed Sensor. I know this is mounted behind the speedo cluster and I believe works off of a spinning reflective wheel or sort to get it readings and send series of pulse voltage to the ECM to determine the vehicle's speed......am I in the ballpark?

Should I get a Code 24 while engine is running, parked and not going down the highway?

Any thoughts, comments, idea will be great and thanks in advance. I have the '81 Service Manual and also the CCC Service Manual and see the troubleshooting chart, just haven't jacked the vette up yet to start that process.