Cruise Descent Control and Deceleration Modes
On vehicles equipped with a Detroit DT12 automated transmission, the functions of the engine brake controls change, depending on which specialty braking mode is being utilized. Two distinct modes can be activated, Descent Control Mode and Deceleration Mode.
Descent Control Mode
Descent Control mode helps control the vehicle and engine speed when descending a grade.
Note: Before engaging Descent Control mode, determine an appropriate speed for the vehicle load and grade of the road.
Note: As a feature of cruise control, descent control mode works with all transmission options; however, cruise control can only request a specific gear if the vehicle is equipped with a DT12. Descent control mode with transmissions other than D12 is therefore limited.
To activate descent control mode:
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Exit cruise control.
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Remove your foot from the accelerator pedal.
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Set the engine brake to any of the three 'on' positions as shown in Fig..
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Use the set or resume buttons to set the vehicle speed.
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Resume cruise control set speed
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Engine Brake Low
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Engine Brake Medium
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Engine Brake High
Fig. 1, Descent Control Mode Engine Brake Positions
The descent control mode active telltale illuminates on the driver display when descent control mode is active. See Fig..
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1.Descent Control Mode Active Telltale
Fig. 2, Descent Control Mode Telltale, ICUC
In descent control mode, all three levels of engine braking are employed to keep the speed below the set speed regardless of the level selected by the right-hand stalk switch.
In the case of very steep road grades, the engine brake may not be able to maintain the vehicle speed. The driver may apply the service brakes without dropping out of descent mode to slow the vehicle. If the vehicle is slowed below the set speed, this lower speed becomes the set speed after the driver releases the service brakes. A pop-up will appear on the instrument cluster screen to notify the driver of the new speed. See Fig.
Fig. 3, New Descent Control Mode Set Speed Pop-Up
When the vehicle's descent is complete, return the engine brake stalk to the OFF/Auto position. At this point the Descent Control set speed will become the new cruise speed.
Descent control mode does not keep the speed above the lower limit of the set speed, so it is possible to eventually coast to a stop, unless the stalk lever is moved to 'off' (position 0), or the accelerator pedal is applied.
After accelerator pedal application, descent control mode is resumed.
Moving the lever to the 0 position deactivates descent control mode and resumes cruise control, using the descent control set speed as the cruise control set speed.
Deceleration Mode
Deceleration mode reduces the vehicle speed at a constant rate.
While in cruise control, activate deceleration mode turning on the engine brake using the right-hand stalk switch as shown in Fig.. The vehicle decelerates at a constant rate until the vehicle comes to a stop, unless the accelerator pedal is applied to override the deceleration, or the right-hand stalk switch is moved to 'off' position.
Moving the lever to 'off' resumes the previously set cruise control speed.