The Latin abbreviation "i.e." is not "ie." I don't think its use is needed in such a simple statement. You are defining a term, not really expressing an idea in different terms.
The use of dashes is not appropriate for a definition either.
I would say "change jobs," not "change his job."
So only sentence 2 is OK for me.
You could also simplify things by stating "He is a car mechanic who decides to change jobs."