The generator matrix

 1  0  0  1  1  1  2  1  1  0  1  1  2  1  1  1  1  2  1  1
 0  1  0  2  1  3  1  0  1  1  2  3  1  2  0  2  0  0  3  1
 0  0  1  1  3  2  1  2  1  2  3  0  3  2  3  0  1  0  3  3

generates a code of length 20 over Z4 who´s minimum homogenous weight is 18.

Homogenous weight enumerator: w(x)=1x^0+10x^18+20x^19+13x^20+8x^21+2x^22+4x^23+1x^24+4x^26+1x^28

The gray image is a code over GF(2) with n=40, k=6 and d=18.
This code was found by Heurico 1.16 in 0.00078 seconds.