Any description to the code? OR it just says "28"? Need more info. If not, you're gonna need a better scanner.

 There are a few things to check. Most common is to check the sensor and it's wiring. If it looks ok, replace the sensor with a good known brand. I have used aftermarket abs speed sensors and they are junk. If that doesn't solve the problem, then it gets a harder. The bearing could be the culprit. If you replace it and it still doesn't work, then I suggest you take it to an expert. Wiring and the ABS module will be tested to make sure they're ok. Again, I have seen aftermarket sensors fail many times. Only sure way to know that it's good is to buy it at the dealer or a get a good known used sensor. Good luck!