RAM 3500 HD Truck 2WD L6-6.7L DSL Turbo (2008)
Hydraulic Control Assembly - Antilock Brakes: Description and Operation
Electronic Variable Brake Proportioning
Description
DESCRIPTION - ELECTRONIC VARIABLE BRAKE PROPORTIONING
Vehicles equipped with ABS use electronic variable brake proportioning (EVBP) to balance front-to-rear braking. The EVBP is used in place of a rear
proportioning valve. The EVBP system uses the ABS system to control the slip of the rear wheels in partial braking range. The braking force of the rear
wheels is controlled electronically by using the inlet and outlet valves located in the integrated control unit (ICU).
Operation
OPERATION - ELECTRONIC VARIABLE BRAKE PROPORTIONING
EVBP is able to decrease, hold and increase rear brake pressure without activating full ABS control. Upon entry into EVBP the inlet valve for the rear
brake circuit is switched on so that the fluid supply from the master cylinder is shut off. In order to decrease the rear brake pressure, the outlet valve for
the rear brake circuit is pulsed. This allows fluid to enter the low pressure accumulator (LPA) in the hydraulic control unit (HCU) resulting in a drop in
fluid pressure to the rear brakes. In order to increase the rear brake pressure, the outlet valve is switched off and the inlet valve is pulsed. This increases
the pressure to the rear brakes.
The EVBP will remain functional during many ABS fault modes. If both the red BRAKE and amber ABS warning indicators are illuminated, the EVBP
may not be functioning.
