206-09A Anti-Lock Control - Traction Control: Description And Operation (page 13 of 17)

ETC attempts to optimize forward traction by reducing engine torque or braking a spinning wheel until it regains grip. 
 
ETC is activated if an individual wheel speed is above that of the vehicle reference speed (positive slip) and the brake 
pedal is not pressed. The spinning wheel is braked, allowing the excess torque to be transmitted to the non spinning 
wheels through the drive line. If necessary, the ABS module also sends a high speed CAN bus message to the ECM to 
request a reduction in engine torque. Torque reduction requests are for either a slow or fast response: a slow response 
requests a reduction of throttle angle (4.0L and 4.4L only); a fast response requests an ignition cut-off (4.0L and 4.4L) or a 
fuel cut-off (2.7L Diesel). 
 
When the DSC function is selected off with the DSC switch, the engine torque reduction feature is disabled. 
 
On vehicles with an automatic transmission, when the ETC function is active the ABS module also signals the TCM to 
prevent gear shifts. 
 

EBA 

EBA assists the driver, in emergency braking situations, by automatically maximizing the braking effort. There are two 
situations when the ABS module will invoke EBA: when the brake pedal is pressed very suddenly and when the brake 
pedal is pressed hard enough to bring the front brakes into ABS operation. 
 
When the brake pedal is pressed very suddenly, the ABS module increases the hydraulic pressure to all of the brakes 
until they reach the threshold for ABS operation, thus applying the maximum braking effort for the available traction. The 
ABS module monitors for the sudden application of the brakes using the inputs from the stoplamp switch and from the 
pressure sensor in the HCU. With the brake pedal pressed, if the rate of increase of hydraulic pressure exceeds the 
predetermined limit, the ABS module invokes emergency braking. 
 
When the brake pedal is pressed hard enough to bring the front brakes into ABS operation, the ABS module increases 
the hydraulic pressure to the rear brakes up to the ABS threshold. 
 
EBA operation continues until the driver releases the brake pedal enough for the hydraulic pressure in the HCU to drop 
below a threshold value stored in the ABS module. 
 

EDC 

EDC prevents wheel slip caused by any of the following: 
 

A sudden decrease in engine torque when the accelerator is suddenly released.  
The sudden engagement of the clutch after a downshift on manual transmission vehicles.  
A downshift using the CommandShift™ on automatic transmission vehicles.  

When the ABS module detects the onset of wheel slip without the brakes being applied it signals the ECM, on the high 
speed CAN bus, to request a momentary increase in engine torque. 
 

HDC 

HDC uses brake intervention to control vehicle speed and acceleration during low speed descents in off-road and low grip 
on-road conditions. Generally, equal pressure is applied to all four brakes, but pressure to individual brakes can be 
modified by the ABS and DSC functions to retain stability. Selection of the HDC function is controlled by the HDC switch 
on the center console. HDC operates in both high and low ranges, at vehicle speeds up to 50 km/h (31.3 mph). 
 
On manual transmission vehicles, HDC may be used in first and reverse gears in high range and all gears in low range. 
Once the vehicle is moving, the clutch pedal should be fully released. The vehicle should not be driven with HDC active 
and the transmission in neutral. 
 
On automatic transmission vehicles, HDC may be used in D, R and CommandShift 1 in high range, and in D, R and all 
CommandShift gears in low range. When in D, the transmission control module will automatically select the most 
appropriate gear. The vehicle should not be driven with HDC active and the transmission in N. 
 
HDC can be selected at speeds up to 80 km/h (50 mph), but will only be enabled at speeds below 50 km/h (31.3 mph). 
When HDC is selected: 
 

At speeds up to 50 km/h (31.3 mph), the HDC information indicator is permanently illuminated if a valid gear is 
selected and, on manual transmission vehicles, the clutch pedal is not depressed.