as usual. The RSC system monitors information from the wheel speed sensors, the throttle position sensor, the steering wheel rotation sensor (steering wheel angle and rate of change) and
a roll-rate sensor (integral to the stability control sensor cluster) that measures changes in vehicle motion. If the RSC system determines from all these inputs that conditions exist for a
potential roll-over event, the system adjusts the brake torque at specific wheels in response to direct measurement of the vehicle roll motion and reduces engine torque to make the vehicle
more stable. By adjusting brake torque, the system can reduce the cornering forces and, therefore, the total roll moment acting on the vehicle. The RSC system can be deactivated by
pressing the stability/traction control switch in the instrument panel.
When the RSC system activates, any of the following can occur:
A rumble or grinding sound much like ABS or traction control
A small deceleration or a reduction in the acceleration of the vehicle
The RSC indicator flashes
If the driver's foot is on the brake pedal, a vibration will be felt in the pedal much like ABS
Some drivers may notice a slight movement of the brake pedal when the system checks itself. The brake pedal moves when an active test of the brake booster is run. During this test a
small amount of pressure is generated at the master cylinder, but no pressure is generated in the brake calipers.
Stability/Traction Control Switch
The stability/traction control switch is hard-wired to the instrument cluster module. The instrument cluster module communicates the stability/traction control switch status to the ABS module
via the HS-CAN bus.
The stability/traction control switch allows the driver to control use of the ESC/RSC and traction control system. This is independent of the ABS function, which cannot be switched OFF by
the driver. The ESC/RSC and traction control system status is indicated by a light in the stability/traction control switch. When the stability/traction control switch is set to OFF, the system is
disabled at and below 32 km/h (20 mph). The system will automatically restore to full functionality every time the vehicle speed exceeds 32 km/h (20 mph) or when the ignition switch is
cycled from OFF to RUN. However, the stability/traction control switch OFF indicator remains illuminated until the switch is pressed a second time. The ABS function continues to work as
designed unless the yellow ABS warning indicator is illuminated. Normal braking function always occurs, unless the red brake warning indicator is illuminated.
Electronic Brake Distribution (EBD)
The HCU is used as an electronic proportioning valve for electronic brake distribution (EBD). The HCU controls the brake fluid pressure to the rear brakes to prevent them from applying
before the front brakes. If ABS is disabled due to DTCs being present in the ABS module, EBD will also be disabled. Instrument cluster failure or a missing instrument cluster message on
the HS-CAN bus will also disable EBD.
Stability Control Sensor Cluster
The sensor cluster (also called inertial module) consists of the yaw rate sensor, roll rate sensor, lateral accelerometer and longitudinal accelerometer. The lateral accelerometer measures
the acceleration which corresponds to the force involved when the vehicle slides sideways. This acceleration has 2 forms. The first is the centrifugal acceleration which is generated when
the vehicle travels around in a circle. The second is the acceleration due to gravity. On level ground there is no contribution from this acceleration. However, if the vehicle is parked
sideways on a bank or incline, the sensor measures some lateral acceleration due to gravity even though the vehicle is not moving.
The longitudinal accelerometer measures the acceleration corresponding to the force involved when the vehicle moves forward and rearward in the horizontal plane, along the centerline of
the vehicle's front and rear wheels.
The yaw rate sensor measures the relative vehicle motion about the vertical axis through its center of gravity.
The roll rate sensor measures the rate of rotation along the front to rear horizontal axis.
Steering Wheel Rotation Sensor
The steering wheel rotation sensor measures the rate of rotation of the steering wheel by monitoring the steering wheel rotation ring as it passes through the sensor gap. The steering wheel
rotation sensor uses 2 signal lines to transmit information to the ABS module about whether the steering wheel is being turned left or right and how far it is being turned. The steering wheel
rotation sensor does not indicate the absolute position of the steering wheel relative to straight-ahead. The stability assist system learns this position by comparing the steering wheel
position with other signals and storing the position it has learned. The stability assist system confirms this position and modifies it as necessary during every new driving cycle.
ABS Module Calibration
If installing a new ABS module, HCU, steering wheel rotation sensor or stability control sensor cluster, the calibration procedure must be carried out. The calibration procedure is required
for the ABS module to learn the "zero-position" of the various ESC/RSC sensors and components.
To calibrate the ABS module, connect the scan tool and carry out the Interactive Vehicle Dynamics (IVD) Initialization sequence.
If a DTC is logged for any component of the ESC/RSC system, the DTC must be cleared or repaired before carrying out the initialization sequence. The need to calibrate the ABS module is
also indicated by the RSC indicator on the instrument cluster module flashing once every 2 seconds. The indicator flashes after clearing the DTCs that are associated with the RSC system.
If a DTC is retrieved after calibration, refer to the ABS Module DTC Chart in this section.
When carrying out the initialization sequence for the ABS module, the vehicle must be on a level surface, must not be moving and the ignition switch must be in the RUN position.
When carrying out the initialization sequence for the ABS module after installing a new steering wheel rotation sensor, the ignition switch must be in the RUN position with the engine
running and the steering wheel must be rotated back and forth from lock position to lock position.
Inspection and Verification
Identifying the Brake System
Two ABS systems are available for this vehicle: standard ABS and ABS enhanced with traction control and stability assist. ABS with traction control and stability assist may also be called
electronic stability control (ESC), roll stability control (RSC), AdvanceTrac®, or interactive vehicle dynamics (IVD) by the scan tool and other service publications.
Vehicles that are equipped with traction control and stability assist can be identified by the presence of individual left and right rear wheel speed sensors.
Vehicles with standard ABS can be identified by the absence of rear wheel speed sensors.
If the vehicle is equipped with standard ABS, refer to Anti-Lock Control in this section to continue diagnosis of this system.
1.
Verify the customer concern.
Page 2 of 6
2008 E-Series Workshop Manual
1/18/2010
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