Antilock Brakes / Traction Control Systems: Description and Operation

Anti-Lock Control

AdvanceTrac(R) With Roll Stability Control (RSC(R))

The AdvanceTrac(R) system is made up of the following systems:

- Conventional ABS
- Traction control
- Electronic Stability Control (ESC)

The Roll Stability Control (RSC(R)) system is an optional feature that works in conjunction with AdvanceTrac(R) to aid in maintaining vehicle stability. AdvanceTrac(R) with RSC(R) system consists of the following components:

- ABS module - attached to the Hydraulic Control Unit (HCU), but can be serviced separately from the HCU.
- Front wheel speed sensors - one sensor is located in each front wheel knuckle. The sensors are serviced separately from the knuckle.
- Front wheel speed sensor magnetic strips - one magnetic strip is located in each wheel bearing and wheel hub assembly and is replaced with the wheel bearing.
- HCU - contains several valves (inlet, outlet, isolation and dump) and a hydraulic pump motor. It is mounted behind the radiator, below the air cleaner assembly. The HCU is replaced as a unit, including the ABS module.
- Rear wheel speed sensors - one sensor is located in each end of the rear axle housing. The sensors are serviced separately.
- Rear wheel speed sensor tone rings - one tone ring is located on each axle shaft.
- Stability control sensors - located inside the Restraints Control Module (RCM) and consist of the following sensors: yaw rate, roll rate, lateral and longitudinal accelerometers. The sensors are integral to the RCM and cannot be serviced separately.
- Steering wheel rotation sensor (6.2L) - located on the end of the steering column near the intermediate shaft. The sensor is serviced separately from the steering column but the sensor ring is replaced with the column. For all other applications, the steering wheel rotation sensor is part of the Electronic Power Assist Steering (EPAS).
- Stability/traction control switch - located in the instrument panel finish panel and is serviced separately from the finish panel.
- Hill descent switch - located in the auxiliary switch panel and is serviced separately.
- Brake vacuum pump (3.5L) - located behind the left headlamp.

Electronic Brake Distribution (EBD)

The ABS module and HCU incorporate a strategy called Electronic Brake Distribution (EBD). The EBD strategy uses the HCU as an electronic proportioning valve to create a balanced braking condition between the front and rear wheels and minimizes the chance of rear wheel lockup during hard braking.

A slight bump sensation may be felt in the brake pedal when EBD is active.

Anti-Lock Control

The anti-lock control system aids in the prevention of wheel lock-up during braking events allowing the driver to maintain steering control and stop in the shortest distance possible under most conditions. This is accomplished by the ABS module and the HCU modulating brake fluid pressure to the affected brake caliper(s).

When the ABS activates, both of the following can occur:

- A rumble or grinding sound may be heard
- If the driver's foot is on the brake pedal, a vibration may be felt in the brake pedal

AdvanceTrac(R) System

Traction Control System

The traction control system aids in the prevention of excessive wheel spin allowing the vehicle to maintain traction during acceleration. This is accomplished by the ABS module and the HCU modulating brake fluid pressure to the affected brake caliper(s) and by the PCM modulating engine torque.

Electronic Stability Control (ESC) System

The ESC system constantly monitors the vehicle's direction of travel relative to the driver's intended course, except when the vehicle is traveling in reverse, and aids in keeping the vehicle traveling along that course. This is accomplished by the ABS module and the HCU modulating brake fluid pressure to the affected brake caliper(s) and by the PCM modulating engine torque.

When the AdvanceTrac(R) system activates, any of the following can occur:

- A rumble or grinding sound may be heard, much like ABS
- If the driver's foot is on the brake pedal, a vibration may be felt in the brake pedal, much like ABS
- A small deceleration or a reduction in the acceleration of the vehicle
- The stability/traction control indicator (sliding car icon) flashes

Roll Stability Control (RSC(R)) System

The Roll Stability Control (RSC(R)) system constantly monitors vehicle roll motion, except when the vehicle is traveling in reverse, and aids in keeping the vehicle stable during sudden or abrupt maneuvers. This is accomplished by the ABS module and the HCU modulating brake fluid pressure to the affected brake caliper(s) and by the PCM modulating engine torque. The combination of reduced engine torque and modulated brake fluid pressure aids in reducing the cornering forces and, therefore, the total roll momentum acting on the vehicle.

When the RSC(R) system activates, the vehicle produces the same noticeable symptoms as it does when the AdvanceTrac(R) system activates.

Traction Control Switch

The stability/traction control switch can be used by the driver to disable and enable the traction control, ESC and RSC(R) systems. Refer to the Owner's Literature.

The conventional anti-lock control system cannot be disabled using the stability/traction control switch.

The systems cannot be disabled when a MyKey(R)-restricted key is in use with the AdvanceTrac(R) always on feature configured to on.

Stability/Traction Control Indicators

There are 2 separate stability/traction control indicators, the stability/traction control indicator (sliding car icon) and the stability/traction control disabled indicator (sliding car icon OFF) located in the Instrument Panel Cluster (IPC). The stability/traction control disabled indicator (sliding car icon OFF) icon is used to alert the driver that the traction control portion of the AdvanceTrac(R) system has been disabled by the driver. This icon only illuminates continuously and does not flash. The sliding car icon is used to alert the driver that a stability/traction event is taking place (flashes twice per second) and to alert the driver of potential concerns in the AdvanceTrac(R) system (illuminates continuously). The IPC message center is a reconfigurable telltale screen which displays messages and indicators including door open/closed messages, Four-Wheel Drive (4WD) system status and AdvanceTrac(R) with RSC(R) system status. When multiple messages need to be displayed, the reconfigurable telltale alternates between all messages.

Trailer Sway Control

Trailer sway control is a unique function in the AdvanceTrac(R) with RSC(R) system that recognizes and aids in reducing trailer sway. The trailer sway control system continually monitors the steering wheel rotation and yaw rate sensors to identify specific, increasing yaw oscillations that occur during a trailer sway event. If the trailer sway event exceeds programmed parameters, the ABS module and the HCU modulate brake fluid pressure to specific brake caliper(s) and the PCM modulates engine torque until the trailer sway is reduced below the programmed parameters.

For vehicles equipped with an optional Trailer Brake Control (TBC) module, the trailer sway control system utilizes the module to apply the trailer brakes to quickly reduce trailer sway.

When the trailer sway control system activates, the vehicle produces the same noticeable symptoms as it does when the AdvanceTrac(R) system activates. In addition, the message center displays TRAILER SWAY, REDUCE SPEED and if the vehicle is equipped with a TBC module, the module shows output to the trailer brakes.

The trailer sway control system only activates when the vehicle speed exceeds 64 km/h (40 mph). The system can be disabled during any key cycle. Refer to the Owner's Literature for information on disabling the system. The system is re-enabled when the ignition is turned to the OFF position and back to the RUN position.

Optimized Hydraulic Braking

Optimized hydraulic braking is a system built into the ABS module to aid in bringing the vehicle to a safe, controlled stop in the event of severe vacuum loss at the brake booster. The ABS module uses a sensor to continually monitor the vacuum in the brake booster. If low vacuum is detected during a braking event, the ABS module activates the pump motor in the HCU to assist with vehicle braking.

Hill Descent Control(TM) (SVT Raptor Only)

Hill Descent Control(TM) can be used to maintain vehicle speed on a downhill grade, operating at speeds between 3 km/h (2 mph) and 32 km/h (20 mph). If the vehicle is on flat or uphill terrain, the system goes into standby mode, remaining activated up to 64 km/h (40 mph). At speeds greater than 64 km/h (40 mph), the Hill Descent Control(TM) system is deactivated. When Hill Descent Control(TM) is active, a rumble or grinding sound may be heard and/or felt.