This paper gives some new theory and design of codes capable of correcting/detecting errors measured under the Lee distance defined over m-ary words, m is an element of IN. Based on the elementary symmetric functions (instead of the power sums), a key equation is derived which can be used to design new symmetric (or, asymmetric) error control algorithms for some new and already known error control codes for the Lee metric. In particular, it is shown that if K is any field with characteristic char(K) = p, p odd, and u, h, n, m = up(h), t is an element of IN are such that n <= (vertical bar K vertical bar - 1)/2 and t <= (p(h) - 1)/2 then there exist m-ary codes C of length n and cardinality vertical bar C vertical bar >= m(n) /vertical bar K vertical bar(t) which are capable of, say, correcting t symmetric errors (i. e., the minimum Lee distance of C is d(Lee)(C) >= 2t + 1) with t steps of the Extended Euclidean Algorithm. Furthermore, if t <= (p - 1)/2 then some of these codes are (essentially) linear and, hence, easy to encode.