Dodge Dakota (ND). Manual - part 118

OPERATION

Accumulators in the valve body store extra fluid released to the system for ABS mode operation. The pump provides
the fluid volume needed and is operated by a DC type motor. The motor is controlled by the ABM.

The valves modulate brake pressure during antilock braking and are controlled by the ABM.

The HCU provides three channel ABS or four channel With Traction Control pressure control to the front and rear
brakes. One channel controls the rear wheel brakes in tandem ABS. The two remaining channels control the front
wheel brakes individually.

During antilock braking, the solenoid valves are opened and closed as needed.

During normal braking, the HCU solenoid valves and pump are not activated. The master cylinder and power
booster operate the same as a vehicle without an ABS brake system.

NOTE: The three modes mentioned below do occur but not necessarily in the order listed everytime.

During antilock braking, solenoid valve pressure modulation occurs in three stages, pressure increase, pressure
hold, and pressure decrease. The valves are all contained in the valve body portion of the HCU.

PRESSURE DECREASE

The outlet valve is opened and the inlet valve is closed during the pressure decrease cycle.

A pressure decrease cycle is initiated when speed sensor signals indicate high wheel slip at one or more wheels. At
this point, the ABM closes the inlet then opens the outlet valve, which also opens the return circuit to the accumu-
lators. Fluid pressure is allowed to bleed off (decrease) as needed to prevent wheel lock.

Once the period of high wheel slip has ended, the ABM closes the outlet valve and begins a pressure increase or
hold cycle as needed.

PRESSURE HOLD

Both solenoid valves are closed in the pressure hold cycle but only the inlet valve is energized. Fluid apply pressure
in the control channel is maintained at a constant rate. The ABM maintains the hold cycle until sensor inputs indi-
cate a pressure change is necessary.

PRESSURE INCREASE

The inlet valve is open and the outlet valve is closed during the pressure increase cycle. The pressure increase
cycle is used to reapply thew brakes. This cycle controls re-application of fluid apply pressure.

REMOVAL

1. Disconnect the battery cables from the battery.

5 - 242

BRAKES - ABS SERVICE INFORMATION