why wont my Pontiac grand am doors lock automatically?

[Andre]

i have a 1999 Pontiac SE and my doors wont lock automatically but they'll unlock just fine

also i think my fuel gauge is broken because every time i start it the fuel gauge will shoot up to full but will slowly go back to where my fuel really is

i dont know why it does this but i'd like to know and how much will it cost to fix these problems