My brake light recently came on and i check the brake fluid resivour and the fluid looks low. Now my question is that should i use original volvo brake fluid oil or should i use this PRESTONE Synthetic brake fluid Dot 4. I bought the prestone oil but im having doubts. Should i put it in or get the "volvo oil"? Also is the prestone SYNTHETIC brake fluid good?

 

If you are going to put in the synthetic fluid you should flush the system and have it in the entire system.
Just topping it off with it won't really do anything but turn the light off.

Also inspect your pads and make sure they aren't low.