Error Code P0500-VSS

Hi-

Does anyone know what the P0500-VSS error is? The code was cleared once but the "service engine soon" light comes on. Is it necessary to fix and if so, how expensive?

Mechanics told me that either

1) Speedometer sensor is faulty (if needle moves to zero and stays there for minutes or so while car is moving, not happening in my case)
OR
2) Speedometer is faulty. (in my case speed displayed seems to be correct)

I wanted to make sure what is the exact problem before getting replace speedometer or sensor.

Any help is appreciated!

Thanks,
-Atul