Electronic Control Module (ECM)
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| Illustration 1 | g06279698 |
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Machine ECM (1) Controller (2) J1 Connector (3) J2 Connector | |
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| Illustration 2 | g06279720 |
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Connectors of Machine ECM (2) J1 Connector (3) J2 Connector | |
The output from the Machine ECM is based on input information from the sensors. The output commands are based on the software programmed into the control module. After the Machine ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the ECM are connected to the machine harness by one 70-pin connector. The inputs and outputs to the ECM can be viewed through the Cat® Electronic Technician (Cat ET) Service Tool. Input and output information can also be viewed using the Operator Monitor.
The ECM also communicates with sensors and other control modules using the CAN Data Link. The data link is bidirectional, allowing the Machine ECM to both receive and send information with the engine.
Note: Only the complete ECM is serviced (no lower levels components). The ECM must be replaced if the ECM is damaged. Replace the ECM if a failure is diagnosed. Most issues are not due to the ECM, and only after a full troubleshooting process should the ECM be replaced.
The Data Link is used to provide a connection for the service tool for troubleshooting, testing, and calibrations. The data link is bidirectional. The data link allows the ECM to receive information. The data link also allows the ECM to send information.
| Machine ECM Connector J1 Contact Descriptions(1) | ||
|---|---|---|
| No. | Type | Pin Description |
| 1 | Ground | LS Return J1-19 (Hyd Lockout Sol) |
| 11 | Output | Stick Retract Solenoid |
| 12 | Output | Stick Extend Solenoid |
| 13 | Ground | Return of PWM J1-11 and J1-12 |
| 19 | Output | Hydraulic Lockout Solenoid |
| (1) | Contacts that are not listed are not used. |
The inputs describe the status of the machine systems. Two types of inputs exist. The inputs can be either a switch type or a sensor type. Switches provide an open, a ground, or a + battery signal to the inputs of the controller. Sensors (frequency, PWM, or voltage) provide a changing signal to the sensor inputs of the controller.
Most sensor input circuits have an internal ECM "pull up voltage" that is present at the ECM contacts. An above normal voltage is internally connected to the ECM input circuit through a resistor. During normal operation, the sensor signal will hold the circuit at a certain signal amplitude. However, conditions such as a loss of power to a component, a disconnection, or an open circuit allow the circuit to be pulled high. The circuit is pulled high by the ECM pull-up voltage. This situation 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 sensor circuits that have pull-up voltage present are:
- Pulse Width Modulated (PWM) sensor input circuits
- Active analog (voltage) input signal circuits
- Passive analog (resistance) input signal circuits
Pulse Width Modulated (PWM) Position Sensor Operation
When powered up, the position sensors continuously send a Pulse Width Modulated (PWM) square wave signal to the ECM. Any movement on a specific axis is detected by the position sensor for that axis. The duty cycle of the PWM sensor signal changes depending on the direction and amount of movement on the axis. The duty cycle is the percentage of time that the signal is high versus the amount of time the signal is low for one cycle. The more time that the duty cycle is high, the greater the percentage of the duty cycle will be.
The percentage of duty cycle signal for a typical position sensor will be recognized as valid is 10 ± 5 to 90 ± 5 percent. These percentages occur the extreme ends of the axis movement. A typical joystick thumbwheel that is in the center or neutral position would result in a duty cycle signal of approximately 50 ± 5 percent. For a foot pedal that is not depressed, a typical duty cycle signal would be 10 ± 5 percent. The duty cycle would be 90 ± 5 percent when the pedal is depressed.
The position sensors are calibrated by the ECM to relate a specific duty cycle signal to a specific axis position for the device being monitored.
The ECM will convert the duty cycle from the position sensor to a calibrated duty cycle signal. The ECM uses this signal and a software "map" to determine the appropriate output signal that will be applied to an output device.
Note: None of the PWM sensors on the machine require manual calibration. The machine ECM will perform an automatic calibration procedure at ECM power-up.
The ECM responds to inputs by sending electrical signals to the outputs. The outputs can create an action or the outputs can provide information to the operator or service technician. The outputs of the ECMs are listed in table 1.
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| Illustration 3 | g06191494 |
Note: The values in Table 2 are for bench testing only. Values may not represent parameters for machine systems specifications.
| Rated Voltage | 12 VDC |
| Coil Resistance | 8.1 ± 0.4Ω (T=20° C) |
The hydraulic lock solenoid is an output of the Machine ECM. The hydraulic lock solenoid is energized to enable the primary hydraulic pressure. The hydraulic lock solenoid is de-energized to disable the primary hydraulic pressure.
This solenoid is activated while the key switch is in the ON position and the hydraulic lock lever is in the UNLOCK position.
Proportional Reducing Solenoids
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| Illustration 4 | g06191521 |
Note: The values in Table 3 are for bench testing only. Values may not represent parameters for machine systems specifications.
| Current | 1.5 A (max at 80° C ambient) |
| Rated Voltage | 12 VDC |
| Coil Resistance | 4.7 ± 0.2Ω (T = 20° C) |
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| Illustration 5 | g06237029 |
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A - Port pressure (kPa) vs Current (mA) | |
The P-Port is blocked and does not allow pressure to the A-port. Therefore, the machine ECM must apply current to the solenoid to send pressure to the A-port of the valve.
Stick Extend/Retract Solenoids
The stick extend and retract solenoids are an output of the Machine ECM. The stick extend and retract solenoids are activated when the joystick is moved to signal those functions.
The data link is a controller network used to pass information back and forth. The data link is designed to carry communications between the various controllers and the monitor. The data link is not a visible component. The network consists of internal control circuits and a wiring harness. The data link is bidirectional. The controllers can receive information and send information. Two 120 Ohm terminating resistors must be installed in the wiring harness in order for each data link to function properly.
An example of how the data link works would be the fuel level information. The fuel level sensor is connected to the machine ECM. The ECM then sends the fuel level information over the data link to the monitor. The monitor uses this information to display the fuel level.