Abelian t-modules are function field analogues of abelian varieties. We study the l-adic Abel-Jacobi map for any abelian t-module E over a function field L of positive characteristic. When the Mordell-Weil theorem (in the sense of Poonen) holds for the L-valued points of E, we show that the Abel-Jacobi map is injective and even an isomorphism when L is finite.