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| Illustration 1 | g03003797 |
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(1) Brake ECM
(2) Engine Speed Sensor (3) Engine Cooling Fan speed Sensor (4) Brake Cooling Pump Speed Sensor (5) Right and Left Front Brake Temperature Sensor (6) Rear Differential Temperature Sensor (7) Cab Air Temperature Sensor (8) Cab Ventilation Duct Temperature Sensor (9) Right and Left Rear Brake Temperature Sensor (10) Keyswitch (11) Cab Air Temperature Dial (12) Left and Right Front Wheel Speed Sensors (13) Left and Right Rear Wheel Speed Sensors (14) Operator TCS Test Switch (15) Retarding Machine Speed Set +/- (16) Brake Pump Pressure Sensor (17) Front and Rear Service Brake Pressure Sensors (18) Left and Right Secondary Brake Pressure Sensors (19) Service Brake Accumulator Pressure Sensor (20) Service Brake Pedal Position Sensor (21) Cab Air Temperature Control Switch (22) AC Low Pressure Switch (23) Brake Filter Switch (24) Brake Cooling Filter Switch (25) Differential Filter Bypass Switch (26) Differential Lube Pressure Sensor (27) Service Brake Pressure Switch (28) Retarder Lever (Position Sensor) (29) Operator ARC Switch (30) Secondary Brake Accumulator Pressure Sensor (31) Secondary Brake Pedal Position Sensor | |
Switches provide information to the electronic control module (ECM). Switches are two state devices. The switches are either open or the switches are closed.
Closed - The switch closes the circuit to ground or the switch closes the circuit to the battery.
Open - the switch opens a circuit to the ECM input.
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| Illustration 2 | g01761597 |
When the key start switch is in the ON position, electrical power from the batteries is supplied to all of the circuits that are affected by the key start switch on the truck.
When the key start switch is in the START position and the conditions for starting the engine are satisfied, the start relay is energized.
"Automatic Retarding Control (ARC)" Switch
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| Illustration 3 | g01950092 |
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The "Automatic Retarding Control (ARC)" switches are located at the base of the center console. (1) "Automatic Retarder Control (ARC) ON/OFF" switch (2) "Automatic Retarder Control UP/DOWN" switch | |
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| Illustration 4 | g01761554 |
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"Automatic Retarding Control (ARC)" switch | |
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| Illustration 5 | g01761555 |
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A view of the "Advisor" screen after ARC switch is engaged. | |
The "Automatic Retarding Control (ARC)" Switch is used in order to select a speed limit for the retarding of the machine. If the ARC switch is in the OFF position, the operator will not be able to set a retarding speed for the machine. When the ARC switch is in the ON position the operator can set a speed limit for the retarding of the machine.
"Retarding Machine Speed Set Accel/Decel" Switch
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| Illustration 6 | g01761053 |
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"ARC Machine Speed Set Accel/Decel" Switch | |
After the "ARC" switch has been set to the ON position, the operator must use the "Set Accel/Decel" switch in order to implement the "ARC" feature. The upper portion of this rocker switch will activate the "SET/ACCEL" function. The lower portion of the rocker switch is used in order to activate the "DECEL" function.
When the operator desires that the ARC control point to be set, the operator will depress the "SET/ACCEL" portion of the rocker switch. The retarding speed of the machine will be set to the engine output speed that corresponds to the speed of the machine. The gear that the operator has set for the machine at that time will be set as the top limit for the drive gear.
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| Illustration 7 | g01761533 |
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View of "Advisor" screen that confirms that the retarding speed has been set | |
The "Advisor" screen will display a popup message for 3 seconds after a retarding speed has been successfully set for the machine. The popup screen on the Advisor will display a value as well as units.
Note: The retarding speed of the machine can only be set when the throttle pedal is NOT DEPRESSED.
After a valid retarding speed has been set for the machine, the operator can toggle the "SET/ACCEL/DECEL" rocker switch in order to raise or in order to lower the retarding speed of the machine. The Advisor will contain a popup display if the operator is incrementing or decrementing the speed of the machine.
Note: The retarding speed of the machine CAN ONLY be adjusted to a speed that corresponds to the maximum retard speed of the engine (typically high idle) and an engine speed that is ABOVE the corresponding downshift breaking points for that gear.
"Operator Traction Control System Test" Switch
The "Traction Control System" monitors the ratio of the speed of each rear wheel in order to detect a slippage in one of the wheels. When a slippage is detected for one of the rear wheels, the secondary brakes will be applied to that wheel in order to apply torque to the wheel with better traction.
The Traction Control System has a dynamic test mode that allows the operator to initiate a test of the Traction Control System while the machine is in motion.
The operator initiates the test by pressing the momentary switch that is located on the dash of the truck. With the TCS test switch is depressed, the TCS system will reduce the cut-in spin ratio to 1.3. Engaging the switch will allow the Traction Control System to engage as the operator performs slight turns of the truck to the left or the right.
The TCS has a semi-automatic test function that allows the operator to monitor TCS solenoid currents as the solenoids are cycled back and forth.
The following conditions must be met before starting this test:
- The truck is stationary (ground speed = 0).
- The service brakes must be applied.
- The parking brake must be released.
- The TCS test switch must be depressed.
The TCS will oscillate the current of each TCS solenoid (right and left) one at a time. The left solenoid is the first one to be engaged as the current is ramped up to the full current and down to no current. The process will then be repeated for the right solenoid and the process will continue to repeat until the TCS test switch is released.
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| Illustration 8 | g01762113 |
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Diagram of typical internal switch | |
The following switches are direct inputs to the Brake ECM. The switches are located within the subsystems of the truck. In order to locate these switches, refer to the System Schematic for the truck.
- Brake Filter Switch
- Brake Cool Filter Switch
- Service Brake Pressure Switch
Differential Filter Bypass Switch
A level 1 event is logged when the filter bypass is detected and the hydraulic oil temperature is greater than 10 seconds.
The pressure switch has a plunger inside the switch that closes the contacts with an acceptable pressure drop across the filter. The pressure switch grounds the signal circuit during normal operation. The plunger of the pressure switch moves in order to allow the pressure switch contacts to open. The pressure switch contacts open when pressure across the filter is greater than the specified value. If the filter is restricted the open pressure switch sends a signal to the Brake ECM. The Brake ECM informs the operator that the filter is restricted or dirty. With a maximum PSI present, the switch will remain closed. When the PSI is at a minimum, the switch will remain open. The circuit for the switch is normally open. The bypass valve will open in order to protect the system if the filter is restricted. The bypass switch provides an input signal to the Brake ECM. The Brake ECM determines if the filter is restricted. The status of the system can be observed by use of the Cat ET program.
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| Illustration 9 | g01761607 |
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Diagram of typical speed sensor | |
The Brake ECM receives input from the following speed sensors:
- Engine Output Speed Sensor
- Left and Right Rear Wheel Speed Sensor
- Brake Cooling Pump Speed Sensor
- Engine Cooling Fan Speed Sensor
The speed sensors output a PWM signal to the Brake ECM. As the gear teeth pass the end of each sensor, an AC voltage is produced. The frequency of the voltage is proportional to the speed of the gear teeth. The Brake ECM uses these signals in order to make decisions concerning the machine components that are being monitored.
The engine cooling system is controlled by the Brake ECM. The Brake ECM varies the engine fan speed after analyzing various inputs such as jacket water temperature, aftercooler coolant temperature, transmission temperature, and ground speed.
The Brake ECM receives input from the following temperature sensors:
- "Right and Left Front Brake Temperature" Sensor
- "Right and Left Rear Brake Temperature" Sensor
- "Rear Differential Temperature" Sensor
The temperature sensors monitor the temperature of the fluids associated with the components that are listed above. An output reading at a higher than expected temperature will result in a signal to the Brake ECM.
The Brake ECM controls the solenoid for the brake cooling pump in order to adjust the flow of oil that is used for the cooling of the brakes. The Brake ECM also directs the flow of oil through extra coolers via the diverter. The coolers provide additional cooling during the automatic retarding control.
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| Illustration 10 | g01762338 |
The Brake ECM receives input from the following pressure sensors:
- Brake Pump Pressure Sensor
- Service Brake Accumulator Pressure Sensor
- Differential Lube Pressure Sensor
- Secondary Brake Accumulator Pressure Sensor
- Front Service Brake Pressure Sensor
- Rear Service Brake Pressure Sensor
- Left and Right Secondary Brake Pressure Sensors
The pressure sensor is a three-wire device. The three wires are the system voltage, ground, and the signal. The source voltage is 24 VDC. The ground is connected to the ground in the Brake ECM. The signal is a frequency input to the Brake ECM for the various components that are listed above.
The signals are pulse-width modulated signals with a fixed frequency of 500 Hz. As the temperatures fluctuate, the duty cycle will fluctuate accordingly.
The Brake ECM also receives information from the service connector via the Cat data link.