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| Illustration 1 | g03389636 |
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(1) Connector view from ECM side
(2) Connector view from harness side | |
The ECM decides based on input information and memory information. After the 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 two 70 contact connectors (J1 and J2). The inputs and outputs to the ECM can be viewed through the Caterpillar Electronic Technician (Cat ET).
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.
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 with 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 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 (MID 057) Contact Descriptions(1) | ||
|---|---|---|
| No. | Type | Function |
| 10 | Cat Data Link + | Cat Data Link + |
| 13 | Battery Return | Battery - |
| 20 | Cat Data Link - | Cat Data Link - |
| 23 | Battery Return | Battery - |
| 24 | Secondary Steering Status | |
| 26 | Switch to Ground Input | ECM Location 0 |
| 31 | Battery Power Input | Battery + |
| 32 | Switch to Ground Input | ECM Location Enable |
| 38 | Battery Power Input | Battery + |
| 44 | Sensor Power Output | 8 V Sensor Supply |
| 45 | Sensor Power Return | 8 V Sensor Return |
| 50 | Sourcing Driver Return | PWM Drivers 1 - 4 Return |
| 54 | Sourcing Driver Return | PWM Driver 11-12 Return |
| 55 | Sourcing Driver Return | PWM Driver 9-12 Return |
| 56 | Sensor Power Return | 10V Sensor Return |
| 57 | Battery Return | Battery - |
| 60 | Sourcing Driver Return | PWM Driver 5-8 Return |
| 69 | Sensory Power Output | 10V Sensor Supply |
| (1) |
| Chassis ECM Contact Description J2(1) | ||
|---|---|---|
| No.(2) | Type | Function |
| 2 | Sourcing Driver Output | Secondary Steering Relay |
| 6 | Sourcing Driver Output | Parking Brake Solenoid |
| 8 | Sourcing Driver Return | Starter Motor Relay / Parking Brake Sol Return |
| 22 | Return | Sensor / Driver Return |
| 28 | PWM Input | Primary Steering Pressure Switch |
| 56 | CAN Data Link + | CAN A Data Link + |
| 63 | Return | Sensor Driver Return |
| 64 | CAN Data Link + | CAN B Data Link + |
| 65 | CAN Data Link - | CAN B Data Link - |
| 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) | |
| (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 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.
Primary and Secondary Steering Pressure Sensor
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| Illustration 2 | g03325148 |
The primary and secondary steering pressure sensors are pulse width modulated sensors. The sensors monitor the pressure in the primary or secondary steering system. The duty cycle of the sensor is proportional to pressure that the sensor measures.
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. This “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 Test Switch
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.
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.
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| Illustration 3 | 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 Chassis ECM, the Implement 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 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 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 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 to broadcast any diagnostic information.