Description And Operation
DESCRIPTION
- Antilock Brake System (ABS) Module
The Electronic Stability Control (ESC) may also be referred to as Electronic Stability Program (ESP) depending on the vehicle model year and configuration. Certain components may also reference ESP, ESC, or use the traction control symbol.
OPERATION
The ABS module (1) is mounted to the Hydraulic Control Unit (HCU) together forming the Integrated Control Unit (ICU). The ABS module is a micro-controller based device which monitors the antilock brake system during normal braking and controls it when the vehicle is in an ABS stop. The ABS function avoids wheels lock during braking maneuvers, maintaining the directionality of the vehicle, and optimizing the reproducibility of stop distance.
The primary functions of the ABS are to:
- Monitor the antilock brake system 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 an ABS mode.
- Store diagnostic information.
- Provide communication to the scan tool while in diagnostic mode.
- Illuminate the ABS, ESC, or BRAKE warning indicator lamp when the system is faulted.
- Illuminate the ESC function lamp when a vehicle dynamic event is occurring.
- Provide vehicle speed information, by monitoring the wheel speed sensors, to all modules on the Controller Area Network-Chassis (CAN-C) bus.
The ABS module constantly monitors the antilock brake system for proper operation. If the ABS module detects a fault, it will disable the ABS system and will command the Instrument Panel Cluster (IPC) to illuminate the amber ABS warning indicator lamp. The normal base braking system will remain operational.
If the vehicle is equipped with traction control, the ESC function lamp will illuminate anytime the amber ABS warning indicator lamp illuminates.
The ABS module 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 ABS module commands the solenoid coils to actuate. The solenoid coils then open and close the valves in the HCU that modulate brake fluid pressure in some or all of the hydraulic circuits. The ABS module continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present. The ABS module contains a self-diagnostic program that monitors the antilock brake system for system faults. When a fault is detected, a warning indicator lamp is turned on and the fault Diagnostic Trouble Code (DTC) is then stored in a diagnostic program memory. A latched fault will disable certain system functionality for the current ignition cycle. An unlatched fault will disable certain system functionality until the fault condition disappears. These DTCs will remain in the ABS module memory even after the ignition has been turned off. The DTCs can be read and cleared from the ABS module memory by a technician using a scan tool. If not cleared with a scan tool, the fault occurrence and DTC will be automatically cleared from the ABS module memory after the identical fault has not been seen during the next 100 ignition cycles.
The ABS module controls the ABS system, Cornering Brake Control (CBC), Motor Schleppmoment Regelung (MSR) (also known as the Drag Torque Control Motor), and Off-Road ABS (ORA) ESC functions. The ESC tries to avoid locking of the wheels for ABS, reduces oversteer tendency for CBC, tries to avoid locking of the drive axle for MSR, and optimally decelerate off-road for ORA.