Engine Brake Operation
To activate the engine brake after the engine is warmed up and the vehicle is in motion:
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Remove your feet from both the clutch and throttle pedals. Press the dash-mounted ENG BRK switch to toggle the engine brake ON. See Fig.. The engine brake will engage at the rate last set on the brake intensity switch.
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Move the intensity switch to the desired intensity. Depending on engine model, LO will provide 1/3 or 1/2 of the full braking capacity of the engine. HI will provide maximum engine braking. Use the dash-mounted switch set at the LO position when driving on flat, open stretches of road. If the service brakes are still required to slow down on a grade, switch to a higher setting on the dash switch, until there is no need for the service brakes. Grade descent speed should be such that the service brakes are used infrequently and that they remain cool, thus retaining their effectiveness.
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For maximum retarding, maintain the top governed speed of the engine through the appropriate selection of gears. When shifting gears, the engine brake will disengage when the clutch pedal is depressed, then engage when the clutch pedal is released.
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To cancel the engine brake application, toggle the ENG BRK switch OFF.
Fig. 1, Cruise Control, Transmission Shift Knob Buttons
If the engine is equipped with both cruise control and an engine brake, the engine brake can operate automatically while in cruise control mode. If the cruise control/engine brake function is turned on in the DDEC VI system programming, the engine brake will come on "low" when the set road speed increases a few miles-per-hour (kilometers-per-hour) above the cruise set speed. The maximum amount of braking (low, medium, high) is selected with the dash switches. When the vehicle returns to the set cruise speed, the engine brake will turn off.
The engine brake will only operate when the accelerator pedal is fully released. Disengaging the clutch will prevent the engine brake from operating.
Vehicles equipped with antilock braking systems (ABS) have the ability to turn the engine brake off if a wheel-slip condition is detected. The engine brake will automatically turn itself back on once the wheel slip is no longer detected. The DDEC VI system will deactivate the engine brake system when the engine speed falls below 1000 rpm or when the vehicle slows down to a preset speed, depending on DDEC programming. This prevents stalling the engine.