Description And Operation - Abs

Courtesy of CHRYSLER GROUP, LLC

1 - Wheel Speed Sensors (WSS)

2 - Integrated Control Unit (ICU)

3 - Instrument Panel Cluster (IPC)

4 - Steering Column Control Module (SCCM)

The Anti-Lock Brake System (ABS) includes the following components:

1.
2.
3.
4.

OPERATION 

The ABS module is mounted to the Hydraulic Control Unit (HCU) together forming the ICU. The ABS module is a micro-controller based device which monitors the anti-lock brake system during normal braking and controls it when the vehicle is in an ABS stop. The ABS function avoids wheel lock during braking maneuvers, maintaining the direction of the vehicle, and optimizing stopping distance.

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, Electronic Stability Control (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 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 anti-lock braking system. The normal base braking system will remain operational.

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 a Diagnostic Trouble Code (DTC) fault 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 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 the identical fault has not been seen during the next 5633 km/h (3, 500 miles). Drive-off may be required for the amber ABS warning indicator lamp to go out on the next ignition cycle.

The ABS has multiple subsystems including, Traction Control System (TCS), Brake Assist System (BAS), Electronic Stability Control (ESC), Hill Start Assist (HSA), Electronic Roll Mitigation (ERM), Trailer Sway Control (TSC), and Hill Descent Control (HDC), Cornering Brake Control (CBC), Drag Torque Control [Motor Schleppmomenten Regelung] (MSR), and Off-Road ABS (ORA) ESC. All of these systems work together to enhance vehicle stability and control in various driving conditions.

A brief explanation of each subsystem follows:

TRACTION CONTROL 

This system monitors the amount of wheel spin of each of the driven wheels. If wheel spin is detected, brake pressure is applied to the slipping wheel(s) to provide enhanced acceleration and stability.

BRAKE ASSIST SYSTEM 

The BAS is designed to optimize the vehicle's braking capability during emergency braking maneuvers. The system detects an emergency braking situation by sensing the rate and amount of brake application and then applies optimum pressure to the brakes.

ELECTRONIC STABILITY CONTROL 

The ESC system enhances directional control and stability of the vehicle using steering wheel angle, yaw (turning) rate and lateral acceleration sensors (combined into Dynamics Sensor). Using signals from these sensors, in addition to individual wheel speed sensor signals the ESC corrects for over/under steering of the vehicle by applying the brake of the appropriate wheel to assist in counteracting an over/under steer condition. Engine power may also be reduced to help the vehicle maintain the desired path. Certain components may also reference ESP, ESC, or use the traction control symbol.

HILL START ASSIST 

The HSA system is designed to maintain the level of brake pressure for a short period of time after the brake pedal is released so that the vehicle does not roll on a hill between releasing the brake pedal and applying the accelerator pedal. The following must be true for HSA to activate:

• The vehicle must be stopped with the brake applied
• The vehicle must be at a eight percent or greater incline (three percent for manual transmissions)
• Gear selection must match uphill direction (forward gear for uphill, reverse for backing uphill)

ELECTRONIC ROLL MITIGATION 

The ERM system monitors steering wheel input and the speed of the vehicle. When the rate of change of the steering wheel angle and vehicle's speed are sufficient to potentially cause wheel lift, the appropriate brake will apply, and engine power may be reduced to lessen the chance that wheel lift will occur. ERM will only intervene during very severe or evasive driving maneuvers.

TRAILER SWAY CONTROL 

The TSC system uses sensors in the vehicle to recognize an excessively swaying trailer and will take the appropriate actions to attempt to stop the sway. The system may reduce engine power and apply the brake of the appropriate wheel(s) to counteract the sway of the trailer. TSC will become active automatically once an excessively swaying trailer is recognized.

HILL DESCENT CONTROL 

The HDC system maintains vehicle speed while descending hills in off-road driving conditions by applying the brakes when necessary. HDC can only be enabled when the transfer case is in the "4WD LOW" position and the vehicle speed is less than 48 km/h (30 mph). If these conditions are not met while attempting to use the HDC feature, the HDC indicator light will flash on/off. The HDC indicator lamp will be on solid when HDC is enabled. When enabled, HDC senses the terrain and activates when the vehicle is descending a hill. HDC is only intended for low speed off-road driving. The accelerator pedal will override HDC at any time.

CORNERING BRAKE CONTROL 

The CBC function reduces the over steer tendency of the vehicle during an ABS braking maneuver in a curve by providing an anti-yaw moment through reduction of front inner wheel pressure. The ESC shall pay attention to possible torque steering disturbance and noise actuations. CBC is active during braking in curve maneuvers or when ABS function is active. CBC is not active when ABS function is not active.

DRAG TORQUE CONTROL [MOTOR SCHLEPPMOMENTEN REGELUNG] 

The MSR function tries to avoid locking of the driving axle during throttle-off maneuvers due to engine braking torque. MSR is active during throttle-off maneuvers. MSR activates when the locking tendency of a driving wheel exceeds the target value.

OFF-ROAD ABS (ORA) ESC 

On deformable surfaces (gravel, sand, etc.), a specific Off-Road ABS calibration with higher wheel slip targets may be used to improve the ABS stopping distance. A larger wheel slip will help take advantage of the wedge effect of the deformable surface in front of the tires. Off-road ABS shall be automatically enabled if the vehicle has terrain switch setting(s) for deformable surfaces, or it may be enabled if the transfer case is switched to low range. The ORA logic may also be used if the ESC detects a deformable surface based on information from the wheel speed sensors, longitudinal acceleration sensor, and brake torque model. The deeper wheel slip targets used in ORA shall be dependent on vehicle speed, steering wheel angle, and surface estimation. The ORA logic is not intended to be used on dry or wet asphalt, packed snow, or ice.

The IPC for this vehicle is located in the instrument panel above the steering column opening. The IPC gauges and indicators are visible through an opening in the cluster bezel and are protected by a clear plastic cluster lens that is secured to the cluster housing by integral latch formations. Several versions of the IPC are offered on this vehicle. These versions accommodate all of the variations of optional equipment and regulatory requirements for the various markets in which the vehicle is offered. The IPC utilizes integrated circuitry and information carried on the CAN C and Controller Area Network-Interior High Speed (CAN-IHS) along with several hard-wired inputs to monitor other sensors and switches in the vehicle. In response to those inputs, the internal circuitry and programming of the IPC allow it to monitor many electronic functions and features of the vehicle. The IPC receives the following:

CAN C Inputs 

• ABS indication lamp ON request
• Key in ignition status
• Commanded ignition switch status

The ICU is located in the left rear corner of the engine compartment near the brake master cylinder. The HCU consists of the ABS module, valve body, pump motor, low pressure accumulators, inlet valves, outlet valves and noise attenuators. Accumulators in the valve body store extra fluid released from the calipers during ABS mode operation. The pump is used to clear the accumulator of brake fluid and is operated by a DC type motor. The motor is controlled by the ABS module. The valves modulate brake pressure during anti-lock braking and are controlled by the ABS module. The HCU provides individual pressure control to each front and rear brake. During anti-lock braking, the solenoid valves are opened and closed as needed. They are cycled rapidly and continuously to modulate pressure and control wheel slip and deceleration. Brake Traction Control and Electronic Stability Program modulate pressure on each wheel individually without any driver brake input. 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. The valves are all contained in the valve body portion of the HCU.

During anti-lock braking, solenoid valve pressure modulation occurs in three stages; pressure increase, pressure hold, or pressure decrease. A brief description of each pressure modulation is as follows:

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 the brakes. This cycle controls re-application of fluid apply pressure.

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 ABS module maintains the hold cycle until sensor inputs indicate a pressure change is necessary.

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 ABS module closes the inlet then opens the outlet valve, which also opens the return circuit to the accumulators. Fluid pressure is allowed to bleed off (decrease) as needed to prevent wheel lock. Once the period of high wheel slip has ended, the ABS module closes the outlet valve and begins a pressure increase or hold cycle as needed.

The ABS module is fused by the Power Distribution Center (PDC).

CAN C Inputs 

• Transfer case status
• Accelerator pedal position (Calculated)
• Static engine torque / Effective engine torque
• Steering wheel angle
• Commanded ignition switch status
• Vehicle speed

CAN C Outputs 

• ABS indication lamp ON request
• Status of any ABS brake event

The SCCM is located near the top of the steering column below the steering wheel. The SCCM includes the Steering Angle Sensor (SAS), the clockspring, lighting multifunction switch, and wiper multifunction switch. The SCCM is secured to the steering column by an integral band clamp on the bottom of the instrument panel side of the SCCM. The SCCM has a centering attachment screw located on the top of the instrument panel side of the SCCM to be certain the SCCM is centered properly on the steering column. The SCCM provides the following:

CAN C Outputs 

• Steering wheel angle

A wheel speed sensor is used at each wheel. The front sensors are mounted to the hub and bearings. The rear sensors are mounted to the park brake assembly. Tone wheels are mounted to the outboard ends of the front and rear axle shafts. The gear type tone wheel serves as the trigger mechanism for each sensor. The sensors convert wheel speed into small digital current signals in amperage. The ABS sends 12 volts to the sensors. The sensor is typically comprised of either a Hall Effect or a Magneto-Resistive element integrated with signal conditioning circuit. The sensor produces signals alternating between two constant levels with frequency proportional to the associated wheel speed. The sensor reads either a toothed ferrous tone wheel or a magnetically charged encoder for signal generation. The signal is sent to ABS module. The WSS provides the following:

CAN C Outputs 

• Wheel RPM for each wheel

Courtesy of CHRYSLER GROUP, LLC

1 - Rear Single Piston Brake Caliper

6 - Front Vented Brake Rotor

2 - Brake Booster

7 - Integrated Control Unit (ICU)

3 - Rear Solid Brake Rotor

8 - Electric Vacuum Pump

4 - Anti-Lock Brake System (ABS) Control Module

9 - Master Cylinder

5 - Front Dual Piston Brake Caliper

The base brake system consists of the following major components:

1. Rear Single Piston Brake Caliper
2. Brake Booster
3. Rear Vented Brake Rotor
4. Anti-lock Brake System (ABS) Module
5. Front Dual Piston Brake Caliper
6. Front Vented Brake Rotor
7. Integrated Control Unit (ICU)
8. Electric Vacuum Pump
9. Master Cylinder

Power assist front disc and rear drum-in-hat disc brakes are standard equipment. Disc brake components consist of front dual piston brake calipers and ventilated rotors, and rear drum-in-hat style brakes with solid rear brake rotors and single piston rear brake rotors.

The parking brake mechanism is lever and cable operated. The cables are attached to actuators on the rear drum-in-hat park brake shoes. The parking brakes are operated by a hand lever.

A dual diaphragm vacuum power brake booster and electric vacuum pump are used for all applications.

All models have an aluminum master cylinder with plastic reservoir.

Factory brake lining on all models consists of an organic base material combined with metallic particles. The original equipment linings do not contain asbestos.

The Electric Vacuum Pump (EVP) system is installed to provide supplemental vacuum to the brake booster when the engine vacuum supply is low. The vacuum pump is connected to the engine and the brake booster through a series of hoses and one-way flow check valves. A vacuum pressure sensor, mounted in the brake booster, provides information to the Anti-lock Brake System (ABS) module, then the vacuum level is sent over the Controller Area Network (CAN) to the Powertrain Control Module (PCM). The PCM modulates the EVP operation to maintain the brake booster vacuum within a given range. This system ensures that the customer experiences a consistent brake pedal feel under all driving conditions.

An electrical connector is used to supply power and ground for the vacuum pump. Operating voltage is between 9V - 16V. Control of the vacuum pump is provided by the PCM using a low side driver to a normally open relay (coil side). The relay coil side power is from a fuse in the under hood Power Distribution Center (PDC). The switched power circuit to the vacuum pump relay is wired directly from the battery through an in-line fuse holder located below the remote battery post connection on the right side in the engine compartment. The relay is located on the left shock tower in the engine compartment.

The ABS module monitors the vacuum pressure sensor and when the signal indicates low engine vacuum the PCM will cycle the vacuum pump as necessary to add vacuum to the power brake booster. The vacuum hoses are connected between the vacuum pump, the engine manifold (for Manifold Absolute Pressure (MAP) sensor signal), and the vacuum pressure sensor (on the brake booster). When the PCM cycles the vacuum pump on, the PCM monitors the MAP sensor and if the vacuum signal does not indicate a rising vacuum then DTCs will be set. Additionally, the Anti-lock Brake System (ABS) module monitors the vacuum at the vacuum pressure sensor and Diagnostic Trouble Codes (DTC)s will also set in the ABS module.