n "ice mode," yes, I'm very familiar with it. Chances are your service manual will not tell you anything about it. I know mine don't. For Bosch systems, I do have the actual Bosch book that they wrote about it. Basically, the computer looks at all of its inputs and tries to figure out of the braking force experienced is exceeding the maximum potential threshold of braking for a conventional surface (negative speed delta exceeds set point). If this happens, it assumes that the wheel(s) in question must have come into contact with a low-mu surface (such as ice), and will prevent excessive brake pressure from reaching the calipers. This hopefully allows the wheel(s) in question to resume spinning, returning some level of control to the driver. However, a problem occurs in racing environments where it's entirely possible to have braking equipment and a road surface so good that your braking exceeds that same set point, causing the ABS to think you're on ice, and thus restricting your braking. It's counterintuitive, but if you release the brake pedal momentarily, you 'reset' this input, allowing you to hit the pedal again and should get full braking pressure back. This system is designed and required for all vehicles registered for public roadway use in the US (and probably elsewhere). It is also mandated that the driver should not be able to disable it. This is why dedicated race vehicles tend to use aftermarket ABS which do not have these "nanny" subroutines programmed. Bosch themselves, for example, offer a race-only ABS that does not have any "ice mode" shenanigans.
The first time I experienced something like this was in a shop heading toward the overhead door. A quick snap of the throttle and immediate brake apply was usually enough to cause tire chirp to alert the guy with the door remote I wanted to leave. While he was playing around looking for the buttons I was quickly learning the car was going to continue to roll toward the door despite repeatedly releasing and applying the brakes. It did eventually stop but the trans was in R at the time.

"Ice Mode" is required by law, so it should be present in all ABS systems regardless of manufacturer.
Once we learned about this issue we played with a number of cars in the parking lot. While we could easily send early ABS equipped Y bodies into "ice mode" the later vehicles and anything with TEVES systems just didn't behave the same way. Years later in a conversation with a Bosch engineer I mentioned this issue. He replied there were software updates to the early Bosch ABS systems and if I had one that seemed overly sensitive a replacement unit should not behave the same way. I have never had a chance to follow up.