206-09A Anti-Lock Control - Traction Control: Description And Operation (page 12 of 17)

SYSTEM OPERATION 

ABS 

ABS controls the speed of all road wheels to ensure optimum wheel slip when braking at the adhesion limit. This prevents 
the wheels from locking, which helps to retain effective steering control of the vehicle. 
 
On the front axle, the brake pressure is modulated separately for each wheel. On the rear axle, brake pressure is 
modulated by select low. Select low applies the same pressure to both rear brakes, with the pressure level being 
determined by the wheel on the lower friction surface. This maintains rear stability on split friction surfaces. 
 

CBC 

CBC influences the brake pressures, below the DSC and ABS thresholds, to counteract the yawing moment produced 
when braking in a corner. CBC produces a correction torque by limiting the brake pressure on one side of the vehicle. 
 

DSC 

DSC uses the brakes and powertrain torque control to help maintain the lateral stability of the vehicle. While the ignition is 
on the DSC function is permanently enabled unless selected off by the DSC switch. Even if DSC is deselected, driving 
manoeuvres with extreme yaw or lateral acceleration may trigger DSC activity to assist vehicle stability. 
 
DSC enhances driving safety in abrupt manoeuvres and in understeer or oversteer situations which may occur in a bend. 
The ABS module monitors the yaw rate and lateral acceleration of the vehicle, and the steering input, then selectively 
applies individual brakes and signals for powertrain torque adjustments to reduce understeer or oversteer. 
 
In general: in an understeering situation, the inner wheels are braked to counteract the yaw movement towards the outer 
edge of the bend; in an oversteering situation, the outer wheels are braked to prevent the rear end of the vehicle from 
pushing towards the outer edge of the bend. 
 
The ABS module monitors the tracking stability of the vehicle using inputs from the wheel speed sensors, the steering 
angle sensor and the yaw rate and lateral acceleration sensor. The tracking stability is compared with stored target data 
and, whenever the tracking stability deviates from the target data, the ABS module intervenes by applying the appropriate 
brakes. On vehicles with an automatic transmission, when the DSC function is active, the ABS module also signals the 
Transmission Control Module (TCM) to prevent gear shifts. If necessary, the ABS module also signals: 
 

The ECM, to reduce engine torque.  
The transfer box control module, to adjust the locking torque of the center differential.  
The rear differential control module, to adjust the locking torque of the rear differential.  

The DSC function overrides the differential locking torque requests from the terrain response system. 
 

EBD 

EBD limits the brake pressure applied to the rear wheels. When the brakes are applied, the weight of the vehicle transfers 
forwards, which reduces the ability of the rear wheels to transfer braking effort to the road surface. This can cause the 
rear wheels to slip and make the vehicle unstable. 
 
EBD uses the anti-lock braking hardware to automatically optimize the pressure of the rear brakes, below the point where 
anti-lock braking would be invoked. Only the rear axle is under EBD control. 
 

ETC 

37 

Yaw rate and lateral acceleration sensor test 

Output 

38 to 40 

Not used 

- 

41 

Stoplamp switch BS contacts 

Input 

42 to 46 

Not used 

-