Q: If a code saying that my fuel sensor switch is not working properly goes unfixed, can it cause other issues later on?

My check engine light came on and I had it diagnosed at Discount Auto. It said that my fuel sensor switch needed replacing. My mechanic refused to replace it because by the time I got my car to him the check engine light was not on and he could not get a code. I have continued to have issues with my cars performance. Lately my car has not wanted to start and when it did it would move very slowly at first. Now I am having other issues with pressure or something building up and have blown off a hose leading to my reservoir tank. Can this be related and what should I do?
My car has an automatic transmission.