Hi,

My brakes havent been working well. Sometimes the pedal will "give" a little to where the pressure I should feel on the brake pedal is not there, and kind of feels jerky. It will also make a small rumbly noise. During this time my brake power is very weak.
My ABS light is also on. I am not sure if these problems are related.
I have been told that the problem I am describing sounds like a master cylinder issue.
I brought my car into Volvo for servicing today and told them the problem as well as the ABS light and I think they only checked the ABS light. They said I need a new control module. I asked would this also make my brakes behave as I described, they said "it could" but somehow I wasnt buying that just based on the way he said it. I paid $90 for this diagnosis and I dont want this to be not the source of my issue.

I guess the help I need is:
a) would an ABS control module failure cause my brakes to behave like this
b) what else does this sound like the problem could be (im sorry if my description sucks, please let me know if it doe and I will try a little harder)
c) since my ABS control module is failing, is this something that I really need to worry about? Will I be unsafe without its function? The cost of repair by dealer is about $900, and the part alone about $400. I am not in a position to handle either cost. Single mom and self-employed.