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| Illustration 1 | g00785019 |
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Electronic control module (ECM) for the Chassis | |
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| Illustration 2 | g01309473 |
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ECM connectors and contacts | |
The Chassis ECM determines outputs based on the input information and memory information. After the Chassis ECM receives the input information the ECM sends a corresponding response to the output. The inputs and outputs of the Chassis ECM are connected to the machine by two 70 contact connectors (J1 and J2). The inputs and outputs to the ECM can be viewed through the Cat® Electronic Technician (Cat® ET).
Note: Only the complete ECM is serviced (no lower level components). The ECM must be replaced if the ECM is damaged. Replace the ECM if a failure is diagnosed.
To aid in diagnostics of certain types of electrical circuits 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 resistor.
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 allows the circuit to be pulled high by the ECM pull-up voltage. This condition results in an above normal voltage condition at the ECM contact. As a result, the ECM activates an FMI 3 (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
To aid in diagnostics of electrical circuits 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 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 allow the circuit to be pulled low by the ECM pull-down voltage. This condition results in a below normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 4 (voltage below normal) diagnostic code for the affected circuit.
| Chassis ECM Contact Description J1 (MID 87) Contact Descriptions(1) | ||
|---|---|---|
| No.(2) | Type | Function/Type |
| 1 | Key Switch (ON) | Battery (+) |
| 10 | Cat Data Link (+) | Cat Data Link (+) |
| 11 | (+) 5V Sensor Supply | Sensor Voltage Supply (+) |
| 13 | Battery (-) | Battery (-) |
| 14 | Key Switch (OFF) | ECM Power (OFF) |
| 19 | CDL/CAN Shield | Shield |
| 20 | Cat Data Link (-) | Cat Data Link (-) |
| 21 | (+) 5V Sensor Supply Return | Sensor Voltage Return (-) |
| 23 | Battery (-) | Battery (-) |
| 26 | ECM Location Code 0 (Ground) | Ground |
| 27 | ECM Location Code 1 (Open) | Open |
| 28 | ECM Location Code 2 (Open) | Open |
| 31 | Battery (+) | Battery (+) |
| 32 | ECM Location Code Enable (Ground) | Ground |
| 38 | Battery (+) | Battery (+) |
| 39 | Battery (+) | Battery (+) |
| 44 | (+) 8V Sensor Supply | Voltage Sensor Supply (+) |
| 45 | (+) 8V Sensor Supply Return | Voltage Sensor Return (-) |
| 46 | Battery (+) | Battery (+) |
| 47 | Battery (+) | Battery (+) |
| 56 | (+) 10V Sensor Supply Return | Voltage Sensor Return (-) |
| 57 | Battery (-) | Battery (-) |
| 60 | PWM Driver Return (1-8) | Sourcing Driver Return |
| 61 | Steering Accumulator Charging Solenoid | Solenoid |
| 64 | Steering Oil Level Sensor (Wiggins) | Analog Active Sensor |
| 67 | Auto Steer Enable Solenoid #2 | (Not Used) |
| 69 | (+) 10V Sensor Supply | Voltage Sensor Supply (+) |
| 70 | Battery (-) | Battery (-) |
| (1) | Contacts that are not listed are not used. |
| (2) | The connector contacts that are not listed are not used. |
| Chassis ECM (MID 87) Contact Description J2(1) | ||
|---|---|---|
| No.(2) | Type | Function/Type |
| 1 | Key Switch (Crank) | Engine Start Input |
| 4 | Solenoid Return | Ground |
| 6 | Steering Accumulator Purge Solenoid | Solenoid |
| 27 | Steering Tank Oil Level Switch | (Not Used) |
| 40 | Steering Accumulator Oil Pressure Sensor #2 | Pulse Width Modulated (PWM) Sensor |
| 41 | Steering Accumulator Oil Pressure Sensor #1 | Pulse Width Modulated (PWM) Sensor |
| 42 | Steering Pump Oil Pressure Sensor | Pulse Width Modulated (PWM) Sensor |
| 56 | Global CAN A + (Redundant Pin) | CAN A Data Link + |
| 57 | Global CAN A Shield (Redundant Pin) | Shield |
| 63 | Ground | Ground |
| 64 | Local CAN B (+) | CAN Data Link (+) |
| 65 | Local CAN B (-) | CAN Data Link (-) |
| 66 | Local CAN B Shield | Shield |
| 67 | Global CAN A + (Main) | CAN A Data Link + |
| 68 | Global CAN A - (Main) | CAN A Data Link - |
| 69 | Global CAN A Shield (Main) | Shield |
| 70 | Global CAN A - (Redundant Pin) | CAN A Data Link - |
| (1) | The ECM responds to an active input only when all 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 required 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.
The ECM measures the voltage that is associated to a specific condition of the control.
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| Illustration 3 | g03330567 |
The hydraulic tank oil level switch (if equipped) is a fluid detection switch. The switch sends a signal showing either the presence or lack of hydraulic oil at a certain level in the system. The switch is used to alert the ECM that hydraulic oil is low.
Steering Pump and Accumulator Pressure Sensor
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| Illustration 4 | g06188019 |
The steering pump pressure sensor is a pulse width modulated (PWM) sensor. The sensor produces a signal. The duty cycle of the signal varies as the condition changes. The frequency of this signal is constant.
The Chassis ECM will respond to the duty cycle of the PWM signal by sending a specific level of electrical current output to the appropriate proportional solenoid valve. The decision is based on the information that is contained in the software of the ECM.
The ECM responds to decisions by sending electrical signals to the outputs. The outputs can create an action or the outputs can provide information to the operator or the service technician.
Pump Accumulator Charging Solenoid
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| Illustration 5 | g01114964 |
These solenoid valves are the proportional type of solenoid valve. The ECM uses a Pulse Width Modulated (PWM) signal to vary the current to the solenoid. The solenoid receives electrical current from the ECM. The solenoid plunger then travels a distance that is in proportion to the electrical current that is sent from the ECM. The electrical current to the solenoid controls the position of the valve. The ECM can detect a failure in the solenoid circuit and the ECM records a diagnostic code when a failure is present.
Note: The solenoid coils are not designed to operate using 24 VDC directly. The ECM sends a PWM signal of 24 V at a duty cycle that will provide the necessary current to the solenoid coils. Do NOT activate the coils by using 24 VDC (+battery). The life of the coils will be reduced drastically. A source of 12 VDC should be used, if the coils must be activated by not using the ECM.
The accumulator purge solenoid is an off and on style solenoid. The ECM sends a signal out to theon/off solenoid that energizes the solenoid to actuate a valve or other function. The accumulator purge solenoid receives a signal from the ECM that causes the solenoid to actuate, moving the solenoid valve to open, and release accumulator pressure oil back to tank.
Electronic communication between the Machine Control ECM, the Implement Control 2 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 two types of data link systems.
- Cat Data Link
- SAE J1939 (CAN) Data Link
The two types of data links are the main structure for communication between all the control modules on the machine.
The SAE J1939 Data Link circuit is mostly used for faster operational communication between the control modules on the machine. The Cat Data Link is used for some of the internal communication that does not require the faster speeds and is used for communication with external devices such as the Cat® Electronic Technician (Cat® ET) service tool.
The Cat Data Link is an input/output of the ECM. The data link uses the connector for the service port to communicate with the Cat Electronic Technician. A data link connection is provided for the product link.
Note: The control for the product link provides a global positioning system for the machine.
The data link is bidirectional. The bidirectional link allows the ECM to input information and output information. The data link consists of the following parts: internal ECM circuits, the related harness wiring, the service tool connector, and the connector for the product link. The Cat Data Link connects to the ECM at contact J1-10 (wire 893-GN(Green)) and contact J1-20 (wire 892-BR(Brown)).
- The ECM receives commands from the Cat ET to change the operating modes. The Cat ET will read the service codes that are stored in the memory of the ECM. Cat ET will clear the service codes that are stored in the memory of the ECM.
- The ECM sends the input and the output information to the Cat ET.
Note: An electronic control module that uses the Cat Data Link will have a module identifier. The MID for the Machine Electronic Control Module is 039.
A data link is required for communication with the service tool (Cat ET) and the electronic control modules as well as instrument clusters and other devices that use this communications protocol. The data link is not used to broadcast any diagnostic information.