The generator matrix

 1  0  0  1  1  1 X^3+X X^3+X^2+X X^3  1  1  1  1  1 X^3+X^2+X  1  1 X^3+X^2  1 X^2+X  1
 0  1  0 X^2 X^2+1  1  1  1 X^3+X^2+X X^3+X^2 X^2+X+1 X^3+1 X^3+X X^3+X+1 X^2 X^3+X^2+1 X^3+X^2+X  1 X^3+X^2+1  1 X^2
 0  0  1 X^2+X+1 X+1 X^2 X^2+1 X^3+X+1  1 X^2+X  X X^3+1 X^2+1 X^3+X^2  1 X^3+X X^2+X X+1 X^3+X^2+X  X X^3+X^2

generates a code of length 21 over Z2[X]/(X^4) who´s minimum homogenous weight is 18.

Homogenous weight enumerator: w(x)=1x^0+136x^18+634x^19+781x^20+1208x^21+570x^22+486x^23+202x^24+68x^25+5x^26+4x^27+1x^30

The gray image is a linear code over GF(2) with n=168, k=12 and d=72.
This code was found by Heurico 1.16 in 0.141 seconds.