Speedometer Problem
 

I have a 1994 Cutlass Ciera 101000 miles. It was parked for 7 months and recently I decided to start driving it again. I charged the battery and checked all the fliuds and when I took it for a drive it acted like the tranny slipped on first shift and the service engine light came on, and the speedometer wasn't working. It set a code PO502 for the variable speed sensor. I was wondering if anyone would know how to test to see if it was the VSS or if it might be another problem. The part isn't that expensive, just want to make sure that's the problem. Any help would be appreciated