I'm pretty sure that the HEV brakes don't use vacuum assist from the ICE (because the petrol engine may not be running - especially under deceleration).crisagatie wrote: ↑Thu Jan 30, 2025 3:02 pm is it possible that the engine stalling caused the loss of pressure in the brake assist system (vacuum) ?
Exactly what it does instead, is of course, subject to the "Official Hyundai/Kia Secrets Act"

I did find this TSB for the Sonata HEV/PHEV & IONIQ EV/HEV/PHEV which has some nice diagrams showing an electrically operated "Pressure Source Unit".
https://static.nhtsa.gov/odi/tsbs/2020/ ... 7-0001.pdf
The Tucson might use the same arrangement...