ATC light

[Mrkentee]

I had it. On mine it was the steering angle sensor, located under the steering wheel, around the steering shaft. 2010 Peterbilt 386.
If it's Bendix, you can download the program for free, and the inline 5 will access it through the ECM port. (Hopefully you have that. If not, most shops do, or somebody on here.)
Once it was replaced it needed to be calibrated, which I could do with my laptop and inline 5.
Hope this helps.