3/31/25, 12:02 AM SIS 2.

2012/01/04 General Information (UENR1136-04)

SMCS - 3121, 4801 i04599072

Brake ECM System PSP

202 -000C
The brake electronic control module (ECM) controls the following braking functions:

Service braking
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Secondary braking

Park braking
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Manual retarding
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Automatic retarder control (ARC) (optional feature)

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Traction control system (TCS) (optional feature)

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The brake ECM also performs monitoring of the system and diagnostic warnings through the
graphical display module.
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Note: The parking brakes are spring-applied. The parking brakes are released by brake oil
pressure that is stored in the secondary brake accumulator. The brake oil pressure in the
secondary brake accumulator is developed when the engine is running.

The parking brakes will engage when any of the following conditions are met:

Keyswitch is in the OFF position.

Direction/speed control is in the PARK position.

The brake oil pressure from the secondary brake accumulator is exhausted.

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Illustration 1 g02776256
Brake ECM components

Service Brake Control

Service braking is performed by pedals which are located on the floor of the cab. The ECM
determines whether the service brakes should engage for the function of ARC or TCS.

Note: The service brakes are applied by brake oil pressure that is stored in the service brake
accumulator. The brake oil pressure in the service brake accumulator is developed when the

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engine is running. The service brakes are released by spring pressure.

Note: Allow the engine to run for 45 seconds before depressing the service brake pedal or
moving the direction/speed control out of PARK. This action will allow the brake accumulators to
charge and provide full braking capacity.

During normal operation, depress service brake control pedal to engage the service brakes. Use
the service brakes for reducing ground speed or for stopping the machine.

The pedal is fully variable. The amount of force that is applied to the brakes is proportional to the
amount of force that is applied to the pedal.

Note: Repeated engagement of the service brakes on downgrades may cause excessive wear
and overheating of the service brakes. Refer to Operation and Maintenance Manual,
"Retarding".

Secondary Brake Control

To avoid the possibility of a unexpected machine movement

when parking on a slope, always block the wheels securely
before leaving the machine unattended.

If the secondary brake system is required in order to stop the

machine, do not operate the machine until a complete check has
been made of the entire braking system and until all necessary
repairs have been made.

The secondary brake pedal is located on the floor of the cab. To modulate the secondary brakes,
the operator presses the secondary brake pedal. Pressing the secondary brake pedal causes
the brake ECM to modulate pressure to the spring-applied brake pack through use of the
secondary brake valve.

Note: The secondary brake system utilizes the parking brake system to apply braking force to
the rear wheels. This system also utilizes the front service brake system to apply braking force to
the front wheels.

In case of failure of the service brakes, depress secondary brake control pedal to engage the
secondary brake system. The amount of force that is applied to the brakes is proportional to the
amount of force that is applied to the pedal.

To obtain the maximum available braking force to the machine in an emergency stop condition,
apply both the service and secondary brake control pedals simultaneously.

Parking Brake Control

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Note: The parking brake is used for parking the truck and is applied by placing the
direction/speed lever in the PARK position. Do not use the retarder levers for parking the
truck.

Parking brake control is performed by the brake ECM. The parking brake is a spring-applied
brake and does not release if hydraulic brake pressure is lost. The parking brakes are released
by brake oil pressure that is stored in the secondary brake accumulator. The brake oil pressure
in the secondary brake accumulator is developed when the engine is running.

The parking brakes will engage when any of the following conditions are met:

Keyswitch is in the OFF position.

Direction/speed control is in the PARK position.

The brake oil pressure from the secondary brake accumulator is exhausted.

Following is the operation of the parking brake:

1. The operator places the shift lever in PARK position.

2. The brake ECM receives the shift lever position from the transmission ECM.

3. The brake ECM completely turns off the secondary brake valve.

4. This action engages the spring-applied parking brakes.

Parking Brake Indicator - When the

parking brakes are applied, the parking
brake indicator will illuminate.

Front Brake Disable Switch

The front brakes and the rear brakes are applied when the service brake pedal is depressed.
Front brake disable switch allows the front brakes to be deactivated. If the front brakes are used
continuously for an extended time, the front brakes can overheat. Under normal circumstances,
the front brake disable switch should be in the OFF position.

ON Position - When the top half of the

front brake disable switch is
depressed, only the rear brakes are
applied when the service brake pedal
is depressed.

Note: When the top half of the front brake disable switch is depressed, the bottom symbol
illuminates to indicate the deactivation of the front brakes.

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OFF Position - When the bottom half

of the front brake disable switch is
depressed, the following occurs:

The front and rear brakes will be applied when the service brake pedal is depressed.

Note: When the bottom half of the front brake disable switch is depressed, the top symbol
illuminates to indicate the activation of the front brakes.

Manual Retarding Control

Manual retarding is performed with a lever located on the steering column. Manual retarding is
performed by energizing the enable solenoid valve and then modulating the left and right
proportional solenoid valves.

Automatic Retarder Control

Automatic retarding is performed by energizing the enable solenoid valve and then modulating
the left and right proportional solenoid valves. ARC can work with the compression brake, which
is controlled by the engine ECM.

Traction Control System

Traction control is performed by energizing the enable solenoid valve and then modulating the
proportional solenoid valve for the side that is slipping. TCS is activated based on the steering
angle of the front wheels, determined by the left steering cylinder position sensor.

Diagnostic Capabilities
The ECM also provides enhanced diagnostics. These diagnostics are available by using
onboard memory. Onboard memory stores the diagnostic codes for retrieval at the time of
service. Service personnel can use the Caterpillar Electronic Technician (Cat ET) service tool for
troubleshooting.

PSP-000CB74D
2025/03/30
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i04599072
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