We prove the non-existence of [gq(4, d), 4, d]q codes for d = 2q 3 − rq 2 − 2q + 1 for 3 ≤ r ≤ (q + 1)/2, q ≥ 5; d = 2q 3 − 3q 2 − 3q + 1 for q ≥ 9; d = 2q 3 − 4q 2 − 3q + 1 for q ≥ 9; and d = q 3 − q 2 − rq − 2 with r = 4, 5 or 6 for q ≥ 9, where gq(4, d) = 3 i=0 d/q i. This yields that nq(4, d) = gq(4, d) + 1 for 2q 3 −3q 2 −3q+1 ≤ d ≤ 2q 3 −3q 2 , 2q 3 −5q 2 −2q+1 ≤ d ≤ 2q 3 −5q 2 and q 3 −q 2 −rq−2 ≤ d ≤ q 3 −q 2 −rq with 4 ≤ r ≤ 6 for q ≥ 9 and that nq(4, d) ≥ gq(4, d) + 1 for 2q 3 − rq 2 − 2q + 1 ≤ d ≤ 2q 3 − rq 2 − q for 3 ≤ r ≤ (q + 1)/2, q ≥ 5 and 2q 3 − 4q 2 − 3q + 1 ≤ d ≤ 2q 3 − 4q 2 − 2q for q ≥ 9, where nq(4, d) denotes the minimum length n for which an [n, 4, d]q code exists.