The generator matrix

 1  1  1  1  1  1  X  X  X  X  X  X
 0 X^2  0 X^2  0 X^2 X^2  0 X^2  0 X^2  0

generates a code of length 12 over Z2[X]/(X^3) who´s minimum homogenous weight is 12.

Homogenous weight enumerator: w(x)=1x^0+13x^12+2x^18

The gray image is a linear code over GF(2) with n=48, k=4 and d=24.
As d=24 is an upper bound for linear (48,4,2)-codes, this code is optimal over Z2[X]/(X^3) for dimension 4.
This code was found by Heurico 1.16 in 0.00036 seconds.