Well from what I remember with talking to someone on the phone with this issue on 2001 trucks (I. E 2nd Gen) the 0573 is not even listed in D/c's Code list. HOWEVER it does not mean it does not exist. You see in 3rd gen rigs it refers to the brake switch much like Bob said above. In the 01 trucks that are equipped with cruise control it has a direct relation to the brake interupt switch that kills the cruise control when the brake is depressed. Now with SOME trucks that use an exhaust brake that needs sensory input from the ecm this can cause it to trip the 0573. It kept throwing the code and he saw I had a BD brake and gave me a holler. His he had wired in. Mine is mechanicly applied (I. E Lift switch under the accel pedal. I simply flip the pedal up with my toe when I want to throw the brake) So I don't throw codes. Some I know use feedback from the ecm to determine delay time etc.