Module, Anti-Lock Brake System (Abs): Operation

WARNING: This page is about a different car, the 2017 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

The primary functions of the Antilock Brake Module (ABM) are to:

Monitor the Antilock Brake System (ABS) and Electronic Stability Program (ESP) for proper operation.
Detect wheel locking or wheel slipping tendencies by monitoring the speed of all four wheels of the vehicle.
Control fluid modulation to the wheel brakes while the system is in ABS or traction control mode.
Modulates fluid pressure to the wheel brakes to control vehicle yaw rate in ESP mode.
Store diagnostic information.
Provide communication to the scan tool while in diagnostic mode.
Illuminate the amber TCS/ESP indicator in the instrument cluster.
Facilitate the function of Hill Start Assist (HSA).

The HSA system is designed to assist the driver in launching a vehicle on an incline. HSA will maintain the level of brake pressure the driver inputs for a short duration once the driver takes his foot off of the brake pedal. If the driver does not apply the throttle during this short duration, the system will release brake pressure and the vehicle will roll down the incline. The system will release brake pressure in proportion to the amount of throttle applied. During operation, HSA will activate the brake control system and a clicking noise may occur. If your foot is on the brake pedal during operation you may feel a slight pedal movement. The clicking and pedal movement is normal and both will stop when HSA becomes inactive. The following criteria must be met in order for HSA to activate: vehicle must be stopped, vehicle must be on an approximate 7% or greater incline, gear selection matches vehicle uphill direction (i.e., vehicle facing uphill is in forward gear; vehicle backing uphill is in REVERSE gear). The system will only work if the intended direction of the vehicle and vehicle gear match. For example, if the intended direction is forward up a hill and the vehicle is in DRIVE and the activation criteria are met, HSA will activate.

The system will work in REVERSE and all forward gears, and will not activate if the vehicle is placed in NEUTRAL.

The ABM constantly monitors the ABS and ESP (if equipped) for proper operation. If the ABM detects a fault, it will turn on the amber TCS/ESP indicator and disable the ABS or ESP if so equipped. The normal base braking system will remain operational at that time.

The ABM continuously monitors the speed of each wheel through the signals generated by the wheel speed sensors to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the ABM commands the ABM solenoid coils to actuate. The coils then open and close the valves in the HCU that modulate brake fluid pressure in some or all of the hydraulic circuits. The ABM continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.