Yes, Crash Imminent Braking requires that you have the Adaptive Cruise Control option installed on the vehicle. They both use many of the same sensors - front facing camera, radar, and ultra-sonic; and much of the same software for computing things such as gap distance, approach rate, braking rate/distance, etc.
Adaptive Cruise Control can be turned On/Off, when it is turned On it has a setting for follow gap distance (Near/Medium/Far). Crash Imminent Braking is an always On "Safety Feature" if Adaptive Cruise Control is installed in the vehicle.
Crash Imminent Braking just like it's name says applies the brakes if it detects an imminent collision with an object - could be a car, person, dog, etc. It does this using the combination of the hardware and software I mentioned above.
I have a 2016 Yukon and the Crash Imminent Braking has gone off 3 times in the couple months since I've had the vehicle. I believe it was warranted in all 3 cases too. In 2 of the 3 instances someone pulled out in front of me and as I was braking the vehicle was also applying the brakes at the same time. The 3rd time someone turned into a driveway in front of me without signaling and as I was slowly braking the vehicle thought it was going to be too close and applied the brakes harder than me. In each case I believe I would've stopped in time without the Crash Imminent Braking assistance, but I'm glad it was there and I'm glad it works the way it does.
I think the system will be very useful in reduced visibility situations - bright sun, fog, rain, etc. when you can't always see the dangers out there. The system also sees everywhere at the same time - left, front, right. If you're distracted by a dog approaching the road on the left side, you may miss the 5 year old running after it from the right side of the road - Crash Imminent Braking will see them both at the same time. How about that same scenario at night when you don't see either - Crash Imminent Braking will still see them both.
I have read a few complaints people have posted about the Crash Imminent Braking, they usually relate to it "going off too much". I tend to think most of these complaints fall into one of two categories - 1)the system was faulty to begin with, 2) they probably aren't the safest drivers in the world and the system is just calling them out on it and they don't like it.
It is a pretty new technology, pretty sure GM released the first rendition in 2014 on the Impala. In it's current state I believe it works very well and will only get better in the future.
