Home » ISX11.9 CM2250 - Service Manual » Cummins ISX11.9 CM2250 – Service Manual 020-999   Vehicle Braking – Overview

Cummins ISX11.9 CM2250 – Service Manual 020-999   Vehicle Braking – Overview

Table of Contents

General Information

General Information

TOC

 CAUTION 

Do not exceed governed engine speed when operating engine brakes. Engine damage can occur. The engine brakes are designed to assist the vehicle’s service brakes in slowing down the vehicle. Never use only the engine brakes to stop the vehicle. If other engine brakes are used, refer to the component manufacturer’s manual.
 
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ISX11.9 engines are equipped with engine brakes. Engine brakes use the energy of engine compression to provide vehicle retardation by converting the engine to an energy-absorbing device that reduces vehicle speed. This is accomplished by a hydraulic circuit that opens the exhaust valves near the end of the compression stroke.

Engine brakes provide the maximum retarding power at rated speed; therefore, gear selection is important.

 
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The amount of braking power available on ISX11.9 engines is up to 390 hp. Braking power is managed by the electronic control module (ECM).

 
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  • Engine brake controls consist of the following:
  • A two-position selector switch
  • An ON/OFF switch
  • A clutch switch
  • A throttle sensor
  • A service brake pressure switch.
 
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Other switches for cruise control that affect engine brake operations are:

  • Cruise Control ON/OFF and SET/RESUME switches (if the Engine Brakes in Cruise Control feature is turned OFF)
  • Service brake air pressure switch.

Engine brakes can operate while Cruise Control is turned ON. Refer to Procedure 019-078 in Section 19.

 
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The engine brake level specifications (two-position switch):

  • Position 1 – 50 percent engine braking power
  • Position 2 – 100 percent engine braking power.
 
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Signals from the ON/OFF switch, the clutch switch, the throttle sensor, and the Cruise/PTO switches are fed into the ECM.

NOTE: Any one of these switches can deactivate the engine brakes. If the Engine Brakes in Cruise Control feature is turned ON, the cruise control/PTO switches will not deactivate the engine brakes.

 
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The ECM then electronically enables or disables the engine brakes.

NOTE: Engine brakes can not be enabled:

  1. When Cruise Control is active and if the Engine Brakes in Cruise Control feature is turned OFF
  2. When engine speed drops below 850 rpm, or 48 kmh [30 mph]
  3. When an electronic fault code is active.
 
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The “throttle sensor” is part of the accelerator pedal assembly, located in the cab, and will deactivate the engine brakes when depressed.

 
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The “clutch switch” uses the motion of the clutch linkage to deactivate the engine brakes when the clutch pedal is depressed. Depressing the clutch while in Cruise Control will disengage the cruise control.

 
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The “service brake pressure switch” is attached to the service brake air supply line.

Applying the service brakes while in Cruise Control will disengage the Cruise Control and enable the engine brakes.

If the Pedal Activated Engine Brake feature is enabled, the service brake pedal must be tapped before the engine brakes will be activated.

 
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Idle the engine 3 to 5 minutes at approximately 1000 rpm to warm the engine before activating the engine brakes. Do not operate the engine brakes until the engine oil temperature is above 30°C [86°F].

 
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To activate the engine brakes, switch the ON/OFF switch to the ON position. Once activated, the operation of the engine brakes is fully automatic.

 
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 WARNING 

Do not use the engine brakes while bobtailing or pulling an empty trailer. With the engine brakes in operation, wheel lockup can occur more quickly when the service brakes are applied, especially on vehicles with single-drive axles.

Make sure the engine brakes are switched to the OFF position when bobtailing or pulling an empty trailer.

 
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 CAUTION 

The engine brakes are designed to assist the vehicle’s service brakes in slowing the vehicle to a stop.

Remember, service brakes are required to bring the vehicle to a stop.

 
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 CAUTION 

Do not use the engine brakes to aid clutchless gearshifting. This can cause the engine to stall or lead to engine damage.
 
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The ECM will disable the engine brakes when engine rpm is below 850 rpm or when an electronic fault code is active.

 
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 CAUTION 

Do not operate the engine if the engine brakes will not deactivate. To do so will cause severe engine damage.

If the engine brakes will not shut off, shut the engine off immediately.

 
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Last Modified:  27-Apr-2010