My 2004 XC90 has the ABS light coming on as well as the brake assistance malfunction message. I connected my code reader and it's not throwing any codes? Is this because I don't have the proper code reader? (I have been able to read codes before on this vehicle) Do I start by pulling off each tire and checking/cleaning the ABS sensors?

 

I decided to pull the sensors and when I got to tire #3 the sensor wire was split on this one. The mounting strap is broke so the wire must have gotten hung up somehow on a another brake/suspension component. I splice the wire and tie wrapped it to the brake caliper.
**You must drive the vehicle for the computer to recognize the fault is fixed and extinguish the ABS light