Volvo: volvo s80, emition, volvo s80

Question
my volvo s80 is a 2000 model. the engine is 2000lit. turbo
before 4 months two massages were shown on the massage screen saying:(1) abs brake failure,stop safely a.s.a.p.(2)emition system service required. These massages come on for some time while driving and then goes away.then they come again and so on.sometimes comes on only the 1 massage or the 2 but more freequently the 1.I went to the garage and they tell me that abs control unit needs to be replaced with a nwe one. also they tell me that it is nessesary to replace  the speed sensor too.
Because the cost was very high i decide not to change anything since the car didnt show any problems while driving.Four months passed and i drive the car with the above situation WITHOUT ANY PROBLEMS WHILE DRIVING.
The quenstion is this:
 IS THERE ACTUALLY A PROBLEM WITH THE ABS SYSTEM,(ABS CONTROL UNIT) AND THE EMITION SYSTEM,OR THE MESSAGES COMES OUT BECAUSE OF ANY OTHER REASON?  

Answer
Yiotis,
Those lights indicate a problem in those systems. The code will need to be read to see what they say. The ABS light would mean that the system needs attention and the Anti lock portion will most likely not work until it is repaired. The brakes themselves will work. Emissions system could be many thing again the codes will show what needs attention.