The generator matrix

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

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+212x^18+512x^19+904x^20+944x^21+849x^22+424x^23+177x^24+32x^25+26x^26+8x^27+6x^28+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 0.125 seconds.