Q: Where is the downhill assist control operation in a car and how is it built?

Hi There, Although this application may vary depending on your specific type of vehicle, generally they all work similarly. The Downhill assist control (commonly referred to as DAC) is a system that helps to control the vehicle without manual operation by the driver when descending down a hill. The DAC system assists engine braking to help improve directional control during descent on steep or slippery surfaces. When in 4WD low range and with DAC activated, if any one wheel accelerates beyond or below a two-to four MPH low-speed setting, the DAC system will control the brakes to help ensure the vehicle continues in a straight position when going down a hill. The DAC system is automatically de-activated if the driver depresses the brake pedal, accelerator pedal, or the DAC button. The active wheel speed sensors enable the operation of the DAC system by determining current road conditions. The system designed to determine current driver operation through an accelerator pedal angle sensor, master cylinder pressure sensor, and the setting of the L4 position switch. DAC next determines its target vehicle speed of two-to-four MPH based on road surface and vehicle driving conditions. When the vehicle accelerates during descent, allowing the vehicle speed to exceed the predetermined speed, DAC is activated. The DAC system will calculate the required brake hydraulic pressure for each wheel, allowing each individual wheel to meet the target vehicle speed. I you need further help with this, please reach out to us here at YourMechanic as we are always here to help.