The ABS fault disappearing when CTIS is unplugged indicates to me that it is probably a programming conflict. The CTIS is connected to the ABS, trans and engine controllers via the J1939 and J1587 data busses. I don’t think there is any actual or planned interaction with CTIS, they simply did it so it was one stop shopping for any programming, access and diagnosis...
If the ABS fault appeared when you plugged in CTIS, then it is probably a version or programming incompatibility, or there is a fault in that CTIS.
If it all of a sudden popped the ABS fault without you doing anything with CTIS, then perhaps it is some failure in the CTIS effecting comms on one of the data busses that the ABS controller is sensitive to.
You need to read the codes to see exactly what it is...
Or, you could disconnect the data buss connections in the CTIS connector and go on with your life as the CTIS operates independently other than receiving a speed signal and driving the overspeed warning light, which it accomplishes directly with hardwired signals with out need of the data busses...