Not quite hill descent control, but rather ABS that prevents wheel lock even when the brakes are not being applied.
I was heading down a wet muddy hill with large, flatting rocks that made the surface very slippery. I had the initial version of my ABS disable switch installed and had the switch pressed for this descent, so the ABS ECU had no way of knowing I was pressing the brakes. Even a light application of the brakes would lock one of the front wheels, which was then immediately released again, even though I kept applying the same amount of brake pressure. The vehicle just kept increasing in speed down the hill and I just had to hold on and try to keep things under control using steering, applying the brakes or not made little to no difference down the steep sections.
This was the type of hill that I would have preferred crawling down as slow as possible, but the ABS didn't allow this. I would, for example, like to slowly step down a rock with the front right wheel locked so that it is dropped down the step and then gains traction on the bottom stopping the vehicle immediately. This isn't possible because the wheel locks as it goes down the step (no traction as it drops down the sheer face), the ABS releases the brakes as it locks, the vehicle moves forward letting the front left get to the step and also drop down. The ABS then releases the front left too which adds to the momentum of the vehicle which then forces the front right to start sliding which the ABS then releases again and so the viscous circle continues.
A similar thing happens while driving at higher speeds on a gravel road. The stopping distance is greatly increased because of the ABS. Yes, you gain more control because the vehicle can be steered, but applying brakes correctly without ABS would still allow steering control to be retained. Also, sometimes it is more important to just stop as quickly as possible without needing to steer. A sudden ditch on a gravel road cannot be steered through, it is better to come to a stop before the ditch even if vehicle steering is compromised!
Anyway, above my reasoning for wanting to disable ABS. Lots of typing and reading, but it forces me to think through the scenarios which helps me understand what I actually want. Thanks!
I had a look at the hydraulic circuit diagram yesterday and it seems I am going to be able to disable the ABS and TC together or disable the TC on it's own, but not the ABS on it's own. I was hoping that I would be able to disable only the ABS, but keep the TC active but it seems this won't be possible. I'll look through the diagrams again this morning and see if I come to the same conclusion as yesterday and then move forward with the PCB design.