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| Illustration 1 | g03307257 |
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(1) Chassis ECM
(2) J1 machine harness connector (3) J2 machine harness connector | |
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| Illustration 2 | g01309473 |
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ECM Connectors and Contacts | |
The Chassis ECM determines actions that are based on input information and memory information. After the Chassis ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the Chassis ECM are connected to the machine harness by two 70 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.
| Chassis ECM Contact Description J1 Contact Descriptions(1) | ||
|---|---|---|
| No.(2) | Type | Function |
| 10 | Cat Data Link + | Cat Data Link + |
| 20 | Cat Data Link - | Cat Data Link - |
| 21 | Sensor Power Return | 5V Sensor Return |
| 24 | Switch to Battery Input | Secondary Steering Motor State |
| 26 | Switch to Ground Input | ECM Location 0 |
| 32 | Switch to Ground Input | ECM Location Enable |
| 39 | Battery Power Input | Battery + |
| 44 | Sensor Power Output | 8 V Sensor Supply |
| 45 | Sensor Power Return | 8 V Sensor Return |
| 46 | Battery Power Input | Battery + |
| 47 | Battery Power Input | Battery + |
| 50 | Souring Driver Return | PWM Drivers 1 - 4 Return |
| 54 | Souring Driver Return | PWM Driver 11-12 Return |
| 55 | Souring Driver Return | PWM Driver 9-12 Return |
| 56 | Sensor Power Return | Battery - |
| 57 | Battery Return | Battery - |
| 60 | Sourcing Driver Return | PWM Driver 5-8 Return |
| 68 | Sourcing Driver Output | Steering System Disable Solenoid |
| 69 | Sensory Power Output | 10V Sensor Supply |
| 70 | Battery Return | Battery - |
| (1) | Contacts that are not listed are not used. |
| (2) | The connector contacts that are not listed are not used. |
| Chassis ECM Contact Description J2(1) | ||
|---|---|---|
| No.(2) | Type | Function |
| 2 | Sourcing Driver Output | Secondary Steering Relay |
| 4 | Sourcing Driver Return | Load Return 1 |
| 8 | Sourcing Driver Return | Load Return 2 |
| 22 | Return | Sensor / Driver Return |
| 26 | PWM Input | Secondary Steering System Steering Switch |
| 34 | PWM Input | Proportional Solenoid Return Feedback 3 |
| 40 | PWM Input | Proportional Solenoid Return Feedback 1 |
| 41 | PWM Input | Proportional Solenoid Return Feedback 2 |
| 49 | PWM Input | Primary Steering Pressure Sensor / Switch |
| 52 | Switch to Ground Input | Secondary Steering Test Switch |
| 56 | CAN Data Link + | CAN A Data Link + |
| 63 | Return | Sensor Driver Return |
| 67 | CAN Data Link + | CAN A Data Link + |
| 68 | CAN Data Link - | CAN A Data Link - |
| 70 | Can Data Link - | CAN A Data Link - |
| (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.
Secondary Steering Motor Status Sensor
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| Illustration 3 | g03319060 |
The ECM monitors the voltage state of the secondary steering motor. The ECM monitors the voltage state by connecting the secondary steering motor status contact on the ECM to the switched terminal on the secondary steering motor relay.
Primary Steering Pressure Sensor
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| Illustration 4 | g03325148 |
The primary steering pressure sensor is a pulse width modulated sensor. The sensor monitors the pressure in the primary steering system. The duty cycle of the sensor is proportional to the pressure that the sensor measures.
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| Illustration 5 | g03330533 |
The steering position sensor is a frequency sensor that determines the angle of the steering system. The sensor sends an electrical pulse down a rod, and a magnetic ring moves up and down the rod as the steering system moves. The time between when the pulse is sent and when the pulse bounces back from the magnet adjust the frequency output of the sensor.
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.
Secondary Steering System Switch
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| Illustration 6 | g03325123 |
The switch is a limit switch that alerts the ECM if the secondary steering system pressure exceeds the switch actuation point. The ECM contact for the switch floats to a high voltage state when the switch is open. When the switch closes, the voltage is pulled to a low voltage state. The switch is normally in a closed position.
Secondary Steering Test Switch
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| Illustration 7 | g03325168 |
The secondary steering test switch is a single pole switch. The switch alerts the ECM that the operator would like to test the secondary steering system. The contact on the ECM for the secondary steering test switch floats to a high voltage state when the switch is open. When the switch is activated and the switch closes, the ECM contact is pulled into a low or ground voltage state.
Steering Tank Oil Level Sensor
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| Illustration 8 | g03330567 |
The steering tank oil level switch is a fluid detection switch. The switch sends a signal showing either the presence or lack of steering oil at a certain level in the system. The switch has a seven second antislosh feature, and is used to alert the ECM that steering oil is low.
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.
Steering System Disable Solenoid
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| Illustration 9 | g03324828 |
The steering system disable solenoid is an On/Off solenoid which locks out the steering system. In the relaxed state of the solenoid, the steering system is active, when the ECM energizes the solenoid, the steering system is disabled.
Note: The solenoid coils are not designed to operate using 24 DCV 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 DCV (+battery). The life of the coils will be reduced drastically. A source of 12 DCV should be used, if the coils must be activated by not using the ECM.
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| Illustration 10 | g03324979 |
The secondary steering relay provides power to the secondary steering motor. The ECM can send a signal to the relay causing the relay to energize. When the relay is energized, battery power is sent to the secondary steering motor.
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 of 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 Caterpillar 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 in order to communicate with the Caterpillar 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 in order to change the operating modes. The Cat ET will read the service codes that are stored in the memory of the ECM. The 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 Caterpillar 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 in order to broadcast any diagnostic information.