I chased this problem for more than a year. I had the ABS unit refurbished by BBA, checked and cleaned sensors, replaced the battery, replaced the ignition switch, replaced the brake pedal sensor, etc... I ended up replacing the steering angle sensor and it immediately fixed all of the problems. I am not saying that is your problem but I am just pointing out that to fix this problem is a methodical process that takes time depending on what is really broken.

Edit: I do want to point it out that if you replace your steering angle sensor, to copy the coding in it BEFORE REPLACING it so you can upload it and code the new unit. I also screen captured all of the menus and data as a backup. If you are not comfortable doing it, take it to an indy or dealer to code.