U0155 Honda - GCM Failure?

Question

I recently took my 2010 Civic to the Honda shop because the dashboard ABS light turned on along with the BRAKE light and a flashing green dot next to the "D" drive (regardless if its on drive or not; its on reverse and still flashes). They said the GCM needed to be changed and that it may or may not solve the problem (if not they would need to change the 2nd of three parts). The GCM alone is almost 2k and I honestly cannot afford it. Is there any way they are mistaken about the GCM or is there any other way i can know for sure what the real problem is? I cannot afford to change the GCM let alone 2 other possible parts over 800 dollars each.

Also is it safe to drive without knowing the true problem. They said since the GCM control the break system that it is not.