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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.
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| Illustration 3 | g03307257 |
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(1) Brake ECM
(2) J1 machine harness connector (3) J2 machine harness connector | |
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| Illustration 4 | g01309473 |
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ECM Connectors and Contacts | |
The Brake ECM determines actions that are based on input information and memory information. After the Brake ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the Brake 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 |
| 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 |
| 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 |
| 4 | Sourcing Driver Return | Load Return 1 |
| 8 | Sourcing Driver Return | Load Return 2 |
| 18 | PWM Input | Ambient Air Temperature Sensor |
| 22 | Return | Sensor / Driver Return |
| 34 | PWM Input | Proportional Solenoid Return Feedback 3 |
| 40 | PWM Input | Proportional Solenoid Return Feedback 1 |
| 41 | PWM Input | Proportional Solenoid Return Feedback 2 |
| 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. |
| Brake ECM Contact Description(1) | ||
| No.(2) | Type | Function |
| 10 | Cat Data Link + | Cat Data Link + |
| 14 | Switch To Battery Input | A/C Mode Switch (Manual) |
| 20 | Cat Data Link - | Cat Data Link - |
| 21 | Sensor Power Return | 5V Sensor Return |
| 22 | Analog Input | Cab Air Temperature Sensor |
| 24 | Switch to Battery Input | A/C Low Pressure Switch |
| 25 | Switch to Battery Input | A/C Mode Switch (Auto) |
| 27 | Switch to Ground Input | ECM Location 1 |
| 29 | Analog Input | Cab Ventilation Duct Temperature Sensor |
| 30 | Analog Input | Evaporator Sensor |
| 31 | Battery Power Input | Battery + |
| 32 | Switch to Ground Input | ECM Location Enable |
| 36 | Analog Input | Operator Temperature Control |
| 38 | Battery Power Input | Battery + |
| 39 | Battery Power Input | Battery + |
| 44 | Sensor Power Output | 8 V Sensor Supply |
| 45 | Sensor Power Return | 8 V Sensor Return |
| 50 | Souring Driver Return | PWM Drivers 1 - 4 Return |
| 54 | Souring Driver Return | PWM Driver 11-12 Return |
| 56 | Sensor Power Return | Battery - |
| 57 | Battery Return | Battery - |
| 60 | Sourcing Driver Return | PWM Driver 5-8 Return |
| 70 | Battery Return | Battery - |
| (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. |
| Brake ECM Contact Description J2(1) | ||
| No.(2) | Type | Function |
| 10 | Sourcing Driver Output | A/C Compressor Clutch Relay |
| 21 | Sinking Driver Output | Cab Air Heater Engine Coolant Actuator |
| 56 | CAN Data Link + | CAN A Data Link + |
| 63 | Return | Ground |
| 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.
Ambient Air Temperature Sensor
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| Illustration 5 | g03319963 |
The ambient air temperature sensor is an active pulse width modulated sensor. The sensor changes the duty cycles as the temperature changes. A lower duty cycle represents a lower temperature and a higher duty cycle represents a higher temperature. The ECM interprets the duty cycle and is able to determine the ambient air temperature.
Recirculation Temperature Sensor
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| Illustration 6 | g03325780 |
The recirculation temperature sensor is a passive sensor located in the return air passage. The sensor creates a different resistance depending on the surrounding temperature. The variations in resistance cause a proportional variation in voltage. This voltage is measured at the ECM contact, and allows the ECM to determine the air temperature.
Cab Ventilation Duct Temperature Sensor
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| Illustration 7 | g03325780 |
The cab temperature sensor is a passive sensor located in the sending air passage. The sensor creates a different resistance depending on the surrounding temperature. The variations in resistance cause a proportional variation in voltage. This voltage is measured at the ECM contact, and allows the ECM to determine the air temperature.
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| Illustration 8 | g03326001 |
The operator temperature control sensor monitors the signal from the temperature control knob on the HVAC panel. This knob sets the operators desired temperature in automatic mode and adjusts the water valve in manual mode. In either mode, the ECM receives a pulse width modulated signal from the knob and HVAC panel that corresponds to a desired temperature or water valve position. The duty cycle is proportional to the position of the knob.
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.
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| Illustration 9 | g03325737 |
The air conditioning mode switch is a two pole switch. The switch has two positions that control the operation of the air conditioning. In the automatic position the ECM controls the operation of the air conditioning to maintain a specified cab temperature. In the manual position, the air conditioning is manually engaged. The ECM has two contacts that pertain to this switch, one signals the ECM the switch is automatic mode, the other signals the ECM the switch is in manual mode. These contacts will float to a high voltage state unless the switch is closed to that contact. When the switch closes to a contact, the contact is pulled to a low or ground voltage state.
Air Conditioning Low Pressure Switches
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| Illustration 10 | g03325964 |
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(1) High-pressure side low-pressure switch
(2) Low-pressure side low-pressure switch (A) To ECM contact (B) To power source entering A/C relay | |
The air conditioning low-pressure contact at the ECM monitors the voltage state of the high and low pressure cut-off switches for the air conditioning. The switches are set up in series from a power source. The switches close and allow power to pass when the pressure in the high pressure and low pressures air conditioning loops is high exceeds the actuation pressure for the switch. If both switches have been actuated, both switches are closed and power flows from the power source to the ECM contact alerting the ECM that the air conditioning circuit is
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.
Air Conditioning Compressor Clutch Relay
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| Illustration 11 | g03323937 |
The air conditioning compressor clutch relay is an electric switch that is controlled by the ECM. The relay controls power to the air conditioning clutch solenoid. When the ECM sends a signal to the relay, the relay activates allowing power to flow to the solenoid, activating the solenoid, and causing the clutch to allow the air conditioning compressor to start.
Cab Air Heater Engine Coolant Actuator
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| Illustration 12 | g03091818 |
The water valve actuator controls the amount of heat that enters the HVAC system. When the water valve actuator is activated, the water valve opens and allows heat from the engine into the heater coils. The water valve is controlled by a pulse width modulated signal from the Machine ECM.
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.