speedo and odometer failer

i got a 99 cavailer rs with the 2.2l and the 3speed auto. last night i was driving and the check engine light came on. also the speedo and odometer are not working. the mil is for code po502 which is the vss low votts but the gas gage is also acting funny (it would go form a full mark to 3/4mark and then back. my ? is were is the vss located on these trans and could a bad ground be casueing these problems.