I started this in an ABS thread, I have an intermittent ATC light. Why on the ABS thread? Well, it is because the coach salesman and the walk-through tech both told me that ATC is "Automatic Traction Control". I asked if it was the switch to turn it off, and they said "No, it enables it. These Allison transmissions only drive one wheel, when you engage ATC, it locks the differential." Now, my hobby is rock crawling (big heavily modified Jeeps), so locking differentials are nothing new to me, and I figured it was a plausible explanation of ATC.
Now I hear it has something to do with fuel filters? Color me confused.
I have an ATC switch on the panel (picture below) and an ATC light on the dash which likes to turn on and off. See switch here at top-right of switches.