Description And Operation
DESCRIPTION
The ABS (Anti-lock Brake System) can also be named the Brake System Module (BSM). Other vehicle lines may reference this module as Electronic Stability Control (ESC), Electronic Stability Program (ESP), or the traction control symbol.
The Anti-lock Brake System (ABS) module (1) is a microcontroller-based device which monitors the anti-lock brake system during normal braking and controls it when the vehicle is in an ABS stop. The Electronic Parking Brake (EPB) module is incorporated into the ABS module. The ABS module also controls Electronic Stability Control (ESC) functions. The ABS module (1) is mounted to a Hydraulic Control Unit (HCU) together forming the Integrated Control Unit (ICU).
OPERATION
The ABS module is mounted to the HCU as part of the ICU. The ICU which includes the ABS module is located in the right front engine compartment forward of the dash panel and inboard of the fender.
The primary functions of the ABS are to:
- Monitor the anti-lock 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 EPB warning indicator lamp when the system is faulted.
- Illuminate the ABS, ESC, or EPB function lamp when a vehicle dynamic event is occurring.
- Provide vehicle speed information, by monitoring the wheel speed sensors, to all modules on the CAN-C and CAN-CH busses.
The ABS module constantly monitors the anti-lock brake system for proper operation. If the ABS module detects a fault, it will turn on a warning indicator lamp and disable the necessary features related to the fault. 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 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 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 anti-lock 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 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 DTC's will remain in the ABS module memory even after the ignition has been turned off. The DTC's 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 40 key cycles with a drive off and no fault.