General Information, Engine Brake
Each engine manufacturer uses a specific engine brake for their engine. Regardless of the manufacturer, the engine brake is operated with the principles outlined here. Refer to the engine manufacturer's operation manual for details of their particular engine brake product.
Warning: To avoid injury from loss of vehicle control, do not activate the engine brake system under the following conditions:
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on wet or slippery pavement, unless the vehicle is equipped with antilock braking system (ABS) and you have had prior experience driving under these conditions;
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when driving without a trailer or pulling an empty trailer;
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if the tractor drive wheels begin to lock, or there is fishtail motion after the engine brake is activated.
Note: When the engine brake is active, the engine brake lamp illuminates in the ICU.
Whenever vehicle braking is required on good road conditions, the engine brake may be used in conjunction with the service brakes. There is no time limit for operation of the engine brake. However, an engine brake does not provide the precise control of, and is not a substitute for, service brakes.
Warning: Usage of the engine brake as the primary braking system can cause unpredictable stopping distances, that could result in personal injury or property damage. Service brakes are the primary vehicle braking system.
Since the engine brake is most effective at rated engine speed, gear selection is very important. Gearing down the vehicle within the limits of the rated engine speed makes the engine brake more effective. Recommended engine braking speed is above 1800 rpm and below the rated speed, which is 950 rpm.
"Control speed" is the speed at which the engine brake performs 100 percent of the required downhill braking, resulting in a constant speed of descent. The control speed varies, depending on vehicle weight and the downhill grade.
For faster descent, select a higher gear than that used for control speed. Service brakes must then be used intermittently to prevent engine overspeed and to maintain desired vehicle speed.
For slower descent, select a lower gear, being careful not to overspeed the engine. Occasional deactivation of the engine brake may be necessary to maintain the designated road speed under these conditions.
If the engine is equipped with both cruise control and an engine brake, the engine brake can operate automatically while cruise control is activated. The maximum amount of braking is selected with the engine brake control. When the vehicle returns to the set cruise speed, the engine brake turns off.
The engine brake only operates when the following conditions are met:
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The accelerator pedal is released.
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The clutch pedal is released (if equipped).
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The engine speed is greater than the rated speed, which is 950 rpm.
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The road speed is greater than 0 mph (programmable).
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The ABS is not active.
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The engine is not in PTO mode.
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The torque converter is in lockup (for automatic transmissions).
Note: The engine brake is disabled when the engine speed is below 850 rpm.
ABS has the ability to turn the engine brake off if wheel slip is detected. The engine brake automatically turns back on once wheel slip is no longer detected.