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| Illustration 1 | g03737502 |
The Machine ECM determines actions that are based on input information and memory information. After the Machine ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the Machine ECM are connected to the machine harness by two 86 contact connectors (J1 and J2). The ECM sends the information to the Caterpillar Electronic Technician (Cat ET) on the Cat Data Link.
Note: The ECM is not serviceable. The ECM must be replaced if the ECM is damaged. Replace the ECM if a failure is diagnosed.
In order to aid in diagnostics of certain types of electrical circuits that are controlled by the ECM, an internal "pull up voltage" is connected to ECM switch and sensor signal input contacts. An above normal voltage is internally connected to the ECM signal input circuit through a resister.
During normal operation, the switch or sensor signal will hold the circuit low or at a certain signal amplitude, however, circuit conditions such as a loss of power to the component, a disconnection, or an open circuit will allow the circuit to be pulled high by the ECM pull up voltage. This condition will result in an above normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 03 (voltage above normal) diagnostic code for the affected circuit.
The types of ECM input circuits that have pull up voltage present are:
- Pulse Width Modulated (PWM) sensor input circuits
- Switch to Ground Input switch input circuits
- Active analog (voltage) input signal circuits
- Passive analog (resistance) input signal circuits
In order to aid in diagnostics of electrical circuits that are controlled by the ECM, an internal "pull down voltage" is connected to ECM switch to battery type input circuits.
During normal operation, the switch contacts that are allowing the connection to a voltage source will hold the circuit high. When circuit conditions such as a loss of power to the switch supply voltage, a disconnection in the switch circuit or an open circuit will allow the circuit to be pulled low by the ECM pull down voltage. This condition will result in a below normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 04 (voltage below normal) diagnostic code for the affected circuit.
| Machine ECM Contact Description J1 Contact Descriptions(1) | ||
|---|---|---|
| No. | Type | Function |
| 2 | PWM Driver | Left Pump Forward Sol |
| 4 | PWM Driver | Left Pump Reverse Sol |
| 5 | Sourcing Driver | Backup Alarm |
| 6 | Sourcing Driver | Hystat Override Sol |
| 9 | Sourcing Driver | Parking Brake Sol |
| 10 | PWM Driver | Right Pump Forward Sol |
| 13 | Return | PWM Driver Return |
| 14 | Return | Switch to Ground Return |
| 21 | Return | On/Off Driver Return |
| 22 | Return | Backup Alarm Return |
| 25 | CAN High | CAN A+ |
| 26 | CAN Low | CAN A+ |
| 29 | Return | 5V Return |
| 30 | Return | 8V Return |
| 34 | Analog Input | Heated Joystick Temperature |
| 35 | PWM Input | Right Track Forward Pressure |
| 36 | Return | 5V Return |
| 37 | PWM Input | Left Track Forward Pressure |
| 38 | PWM Input | Right Track Reverse Pressure |
| 41 | PWM Input | Left Track Reverse Pressure |
| 42 | PWM Input | Decelerator Pedal Sensor |
| 44 | Switch to Ground | Service Brake Pedal Switch N/C |
| 49 | Return | 8V Return |
| 50 | Switch to Ground | Traction Assist N/O |
| 54 | Switch to Ground | Traction Control N/C |
| 55 | Switch to Ground | Traction Control N/O |
| 56 | 8V Supply | Hystat Pressure Sensor |
| 57 | PWM Driver | Right Pump Reverse Sol |
| 60 | Switch to Ground | Traction Assist N/C |
| 62 | Switch to Ground | Service Brake Pedal Switch N/O |
| 64 | 5V Supply | Track Speed Sensor |
| 65 | PWM Driver | Left Motor Sol |
| 67 | Switch to Ground | Park Brake N/C |
| 68 | Switch to Ground | Park Brake N/O |
| 70 | PWM Input | Hystat Joystick FNR Sensor |
| 71 | PWM Input | Accel/Decel Thumbroller |
| 74 | Switch to Ground | Heated Joystick SW GND=OFF |
| 75 | Switch to Ground | Heated Joystick SW GND=HIGH |
| 81 | Battery | Battery - |
| 82 | Battery | Battery - |
| 83 | Battery | Battery - |
| 84 | Battery | Battery + |
| 85 | Battery | Battery + |
| 86 | Battery | Battery + |
| (1) | Contacts that are not listed are not used. |
| Machine ECM Contact Description J2(1) | ||
|---|---|---|
| No.(2) | Type | Function |
| 3 | PWM Driver | Right Motor Sol |
| 7 | Return | PWM Driver Return |
| 10 | Return | PWM Driver Return |
| 23 | CAN A High | CAN A+ |
| 31 | CAN A Low | CAN A - |
| 38 | PWM Input | Throttle PWM Sensor |
| 40 | CAN B Low | CAN B- |
| 43 | PWM Input | Right Speed Sensor A |
| 44 | PWM Input | Right Speed Sensor B |
| 46 | PWM Input | Left Speed Sensor A |
| 48 | CAN B High | CAN B+ |
| 50 | PWM Input | Left Speed Sensor B |
| (1) | The ECM responds to an active input only when all of the necessary conditions are satisfied. |
| (2) | The connector contacts that are not listed are not used. |
The machine has several different types of input devices. The ECM receives machine status information from the input devices and determines the correct output action that is needed in order to control machine operations based on memory and software parameters. The machine utilizes the following types of inputs: switch type and sensor type.
Switches provide signals to the switch inputs of the ECM. The possible outputs of a switch are listed: an open signal, a grounded signal and + battery signal.
Sensors provide an electrical signal to the ECM that constantly changes. The sensor input to the ECM can be one of several different types of electrical signals such as: pulse width modulated (PWM) signals, voltage signals and frequency input signals. Each possible input to the ECM is listed in the tables for the 70-pin connectors.
Inputs provide information to the ECM in the form of sensors or switches.
Sensors provide information to the ECM about the intent of the operator or changing conditions. The sensor signal changes proportionally to the changing of operator input or changing conditions. The following types of sensor signals are used by the ECM.
Frequency - The sensor produces a signal and the frequency (Hz) varies as the condition changes.
Pulse width modulated - The sensor produces a signal. The duty cycle of the signal varies as the condition changes. The frequency of this signal is constant.
Analog - The ECM measures the voltage that is associated to a specific condition of the control.
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| Illustration 2 | g01339854 |
The ECM increases the desired speed of the machine when the thumb switch is moved away from the operator. The ECM decreases the desired speed of the machine when the thumb switch is moved toward from the operator.
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| Illustration 3 | g03737917 |
The electrohydraulic control system has a two axis joystick as the operator interface. The joystick is used in order to supply direction and steering commands. The longitudinal displacement of the joystick will control the forward and the reverse direction of the machine. The lateral displacement of the joystick will provide the steering control. The steering sensor of the joystick (1) provides a 500 Hz PWM signal and the joystick F/N/R sensor (2) provides a 500 Hz PWM signal. The signal is proportional to the joystick sensor position for each axis. The range of the sensor in the longitudinal axis is nominal at 27% at the full forward position to 3% at the full reverse position. The range of the sensor in the lateral axis is nominal at 3% at the full left position to 7% at the full right position.
Speed Sensor (Left Track)
Speed Sensor (Right Track)
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| Illustration 4 | g03794651 |
A track speed sensor is integrated into the output stage of the hydrostatic drive motors. The sensor provides two square wave signals that are 90 degrees out-of-phase and the frequency remains proportional to motor speed while the amplitude remains constant. These signals are used in order to calculate both the track speed and the direction of rotation. The sensors require a regulated 5 V power supply.
Brake Pedal and Deceleration Pedal
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| Illustration 5 | g03737957 |
The position sensors inform the ECM of the position of the pedal that is controlled by the operator. The position sensor outputs a pulse width modulated signal. The duty cycle of the signal will vary in proportion to the position of the pedal. These PWM signals are inputs to the ECM. The ECM uses the signals in order to determine the position of the pedal. The frequency of this signal is constant at approximately 500 Hz. The ECM provides a 10 V supply to the sensor.
The position sensor for the pedal continuously informs the ECM of the position of the pedal. The ECM uses the duty cycle of the signal in order to determine the position of the pedal. The ECM uses the position of the pedal in order to control the braking of the transmission. The ECM also uses the position of the pedal to control the engine deceleration if the parameter is configured. See Systems Operation Section, "Configuration Parameters" for more information.
If the pedal is pressed past a specific point, the ECM will apply the parking brake. The duty cycle of the sensor decreases as the pedal is depressed.
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| Illustration 6 | g03737979 |
This sensor is an PWM sensor that informs the ECM of the hydrostatic oil pressure within the drive loop of the hydrostatic transmission. The ECM measures a voltage that is associated to the pressure in the drive loop. This information is used in order to maintain an optimal pressure in the drive loop during machine operation.
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| Illustration 7 | g03737990 |
This sensor is an analog sensor that informs the ECM of the fuel level in the fuel tank. The ECM measures a voltage that is associated to the level of the fuel inside the tank.
Switches provide an open signal, a ground signal, or a +battery signal to the inputs of the ECM. Switches are open or closed.
- When a switch is open, no signal is provided to the corresponding input of the ECM. The “no signal” condition is also called “floating”.
- When a switch is closed, a ground signal or a +battery signal is provided to the corresponding input of the ECM.
Brake Pedal and Deceleration Pedal (Limit Switch)
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| Illustration 8 | g01339845 |
The switch is a limit switch that is mounted on the pedal assembly of the brake. The pedal provides an input to the ECM that controls the braking of the transmission and the control of the parking brake solenoid. When the pedal is fully depressed, the switch is closed indicating that the operator is requesting the application of the parking brake. The pedal can be configured to decrease both engine speed and track speed, or track speed only. The configuration parameters are set in ET.
The parking brake switch has a normally open contact and a normally closed contact. The contacts provide switch to ground inputs to the ECM. When the ECM determines that the parking brake switch has been engaged and the machine is in motion, the ECM will fully upstroke the motors and the ECM will fully destroke the pumps. Then, the ECM will apply the parking brake. The switch is a momentary switch, and pressing the switch toggles the activation of the parking brake.
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| Illustration 9 | g01339851 |
The switch has a normally open contact that connects to the ECM at contact J1-42. The switch has a normally closed contact that connects to the ECM at contact J1-41. The contacts provide switch to ground inputs to the ECM in order to indicate the position of the switch. When the switch is pressed, the ECM engages the speed recall.
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| Illustration 10 | g02722693 |
The throttle switch has four signal connections and one ground. During operation of the throttle switch, one or more of the signal connections will be switched to ground, while the remaining connections will be held high by the ECM internal pull-up voltage. The machine ECM will associate a specific engine speed with each combination of signal inputs that are grounded. The Machine ECM will send the requested engine speed information to the Engine ECM.
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| Illustration 11 | g01339852 |
This switch activates the horn.
Solenoid Valve (Parking Brake)
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| Illustration 12 | g03795047 |
The parking brake solenoid valve disengages the brakes. The brakes are applied by a spring and released by pressure. When the operator activates the parking brake switch, the ECM disengages the parking brake solenoid valve which relieves the hydraulic pressure and the brakes are applied. The brakes are released when the solenoid is engaged. The solenoid is always disengaged when the neutral interlock is active. The neutral interlock must be released and the transmission joystick is not in neutral in order for the parking brake solenoid to be engaged. The solenoid will not be engaged under the following conditions:
- The parking brake lockout configuration is locked.
- A stall test is attempted
- The electronic pressure override calibration is attempted.
Transmission Pilot Supply Solenoid
The transmission pilot supply solenoid provides pilot oil to the hydrostatic pumps. The ECM only engages the transmission pilot supply solenoid if the neutral interlock has been cleared. If the transmission pilot supply is not energized, there is no oil to the transmission and the machine cannot be moved. The ECM also disengages this solenoid during a fault that requires the machine to shut down.
Note: The machine is equipped with a Neutral interlock . The Neutral interlock prevents the machine from starting when the Forward, Neutral, and Reverse (FNR) switch is not in the Neutral position. When the machine is running, the parking brake will not release unless the FNR switch is in the Neutral position.
Solenoid Valves (Pump and Motor Displacement Control)
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| Illustration 13 | g03795173 |
Forward Solenoid for the Left Drive Pump
Reverse Solenoid for the Left Drive Pump
Reverse Solenoid for the Right Drive Pump
Forward Solenoid for the Right Drive Pump
Proportional Solenoid of the Right Drive Motor
Proportional Solenoid of the Left Drive Motor
The four solenoid valves for the drive pumps are outputs of the ECM. The ECM uses these solenoid valves to control the speed and the direction of the machine by varying the pump displacement. The two solenoid valves for the drive motors are outputs of the ECM. The ECM uses these solenoid valves to control the machine speed by varying the motor displacements. The ECM applies electrical current to the appropriate solenoid valves. This electrical current is based on the information from the following devices:
- The Joystick forward/neutral/reverse Position
- The Joystick Thumbroller Position
- The Joystick Steering Position Status
- The Parking Brake Switch
- The Engine Speed Sensor
- The Left Track Speed Sensor
- The Right Track Speed Sensor
- The Brake/Decel Pedal
- The Travel Pressure Sensors
The solenoid valves are pressure reducing valves. The solenoids are the proportional type. The ECM uses a pulse width modulated signal (PWM) to vary the current to the solenoid. The current varies the pressure output of the solenoid valve. The amount of pressure controls the swashplate angle of the pumps and motors.
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| Illustration 14 | g03738053 |
The start relay is an on/off solenoid that controls the starting motor. When the relay is not energized, the starting motor is not running. When the relay is energized, the starting motor is running.
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| Illustration 15 | g00391203 |
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Backup Alarm | |
The backup alarm is an output of the ECM. The backup alarm alerts nearby personnel that the machine is backing up. When the operator selects the REVERSE position, the ECM energizes the backup alarm.
Electronic communication between the Implement ECM, Machine ECM, Engine ECM, and the other control modules on the machine is conducted over data link circuits. The data link circuits allow the sharing of information with other electronic control modules. The data link circuits are bidirectional. The data link circuit allows the ECM to send information and to receive information.
The electronic communication system consists of multiple CAN datalink systems.
The SAE J1939 CAN Data Link circuit is separated into different groups. "CAN A" is connected to all of the ECMs on the machine, and is used primarily for information and service purposes, such as the Caterpillar Electronic Technician (CAT ET). The other data link systems are high speed data links used for machine control purposes.