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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.
Inorder 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
Inorder 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.(2) | Type | Function |
| 2 | Differential Speed Input + | Engine Speed Sensor + |
| 3 | Differential Speed Input - | Engine Speed Sensor - |
| 6 | Differential Speed Input + | Intermediate Speed Sensor + |
| 7 | Differential Speed Input - | Intermediate Speed Sensor - |
| 8 | Differential Speed Input + | Torque Converter Speed Sensor + |
| 9 | Differential Speed Input - | Torque Converter Speed Sensor - |
| 10 | Cat Data Link + | Cat Data Link + |
| 11 | Sensor Power Output | 5V Sensor Supply |
| 13 | Battery Return | Battery - |
| 15 | Differential Speed Input + | Transmission Speed Output Sensor 1 + |
| 16 | Differential Speed Input - | Transmission Speed Output Sensor 1 - |
| 17 | Differential Speed Input + | Transmission Speed Output Sensor 2 + |
| 18 | Differential Speed Input - | Transmission Speed Output Sensor 2 - |
| 20 | Cat Data Link - | Cat Data Link - |
| 21 | Sensor Power Return | 5V Sensor Return |
| 22 | Analog Input | Torque Converter Oil Temperature Sensor |
| 23 | Battery Return | Battery - |
| 26 | Switch to Ground Input | ECM Location 0 |
| 30 | Analog Input | Transmission Oil Temperature Sensor |
| 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 |
| 47 | Battery Power Input | Battery + |
| 48 | Sourcing Driver Output | Transmission Solenoid 1 |
| 50 | Sourcing Driver Return | PWM Drivers 1 - 4 Return |
| 51 | Sourcing Driver Output | Transmission Solenoid 5 |
| 52 | Sourcing Driver Output | Transmission Solenoid 7 |
| 55 | Sourcing Driver Return | PWM Driver 9-12 Return |
| 56 | Sensor Power Return | 10V Sensor Return |
| 57 | Battery Return | Battery - |
| 58 | Sourcing Driver Output | Transmission Solenoid 2 |
| 59 | Sourcing Driver Output | Transmission Solenoid 3 |
| 60 | Sourcing Driver Return | PWM Driver 5-8 Return |
| 61 | Sourcing Driver Output | Transmission Solenoid 4 |
| 62 | Sourcing Driver Output | Transmission Solenoid 6 |
| 64 | Switch to Ground Input | Transmission Charge Filter Bypass Switch |
| 65 | Sourcing Driver Output | Differential Lock Solenoid |
| 69 | Sensory Power Output | 10V Sensor Supply |
| (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 |
| 22 | Return | Sensor / Driver Return |
| 32 | PWM Input | Left-Hand Wheel Speed Sensor |
| 33 | PWM Input | Right-Hand Wheel Speed Sensor |
| 35 | PWM Input | Shift Lever Sensor |
| 37 | Switch to Ground Input | Engine Retarder Lever High |
| 38 | Switch to Ground Input | Engine Retarder Lever Medium |
| 39 | Switch to Ground Input | Engine Retarder Lever Low |
| 52 | Switch to Ground Input | Differential Lock 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) | 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 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.
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| Illustration 3 | g03425321 |
The ECM receives signals from the engine speed sensor as a frequency signal. The engine speed sensor is a passive sensor. The signal indicates the rotational speed of the connection from the output of the engine to the input of the torque converter. The signal is generated by a gear passing in front of the sensor, with one full pulse generated per tooth on the gear. The sensor has an inductive coil that creates a voltage pulse to the ECM when a gear tooth passes the sensor. The ECM interprets the frequency of the pulses as the speed of the gear.
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| Illustration 4 | g03425321 |
The ECM receives signals from the intermediate speed sensor as a frequency signal. The intermediate speed sensor is a passive sensor. The signal indicates the rotational speed of the connection from the output of the first set of clutches (one, two, and three) in the transmission and the second set of clutches (four, five, and six). The signal is generated by a gear passing in front of the sensor, with one full pulse generated per tooth on the gear. The sensor has an inductive coil that creates a voltage pulse to the ECM when a gear tooth passes the sensor. The ECM interprets the frequency of the pulses as the speed of the gear.
Torque Converter Output Speed Sensor
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| Illustration 5 | g03425382 |
The ECM receives signals from the torque converter speed sensor as a frequency signal. The torque converter sensor is a passive sensor. The signal indicates the rotational speed of the output of the torque converter to the input transmission. The signal is generated by a gear passing in front of the sensor, with one full pulse generated per tooth on the gear. The sensor has an inductive coil that creates a voltage pulse to the ECM when a gear tooth passes the sensor. The ECM interprets the frequency of the pulses as the speed of the gear.
Transmission Output Speed Sensors
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| Illustration 6 | g03319339 |
The ECM receives signals from the transmission output speed sensors as a frequency signal. The transmission output speed sensors are passive sensors. The signal indicates the rotational speed of the output shaft of the transmission. The signal is generated by a gear passing in front of the sensor, with one full pulse generated per tooth on the gear. The sensor has an inductive coil that creates a voltage pulse to the ECM when a gear tooth passes the sensor. The ECM interprets the frequency of the pulses as the speed of the gear.
Torque Converter Oil Temperature Sensor
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| Illustration 7 | g03425409 |
The torque converter oil temperature is a passive analog sensor. The sensor has an internal resistance that varies as the temperature of the torque converter oil changes. The ECM detects the changes in resistance as a voltage drop and by this voltage, determines the temperature of the torque converter oil.
Transmission Oil Temperature Sensor
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| Illustration 8 | g03425409 |
The transmission oil temperature is a passive analog sensor. The sensor has an internal resistance that varies as the temperature of the transmission oil changes. The ECM detects the changes in resistance as a voltage drop and by this voltage, determines the temperature of the transmission oil.
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| Illustration 9 | g03329309 |
The wheel speed sensors are used to determine the rotational speed of the wheels. The speed sensors are active sensors and send pulse width modulated signals to the ECM. The sensor sends one pulse per tooth edge. The ECM uses the information for Tire Spin Reduction Control and Differential Lock Engagement Protection Control.
Transmission Shift Lever Sensor
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| Illustration 10 | g03886344 |
The transmission shift lever sensor is a pulse width modulated sensor located in the base of the shift lever. The sensor changes the duty cycle of a pulse width modulated signal based on the position of the lever. Table 3 shows the duty cycle percentages at different shift lever positions. The ECM interprets the duty cycles as operator requests for specific gear positions.
| Position | Duty Cycle |
| "D" | 16% ± 4% |
| "2" | 32% ± 5% |
| "1" | 56% ± 5% |
| "N" | 80% ± 5% |
| "R" | 90% ± 2% |
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 11 | g03886344 |
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(1) Top gear switch
(A) Connector A (B) Connector B | |
The transmission top gear switch (1) is a single pole switch that controls the top gear limit feature. The switch normally is open and the ECM contact floats to a high-voltage state. When the switch is closed, the ECM contact is pulled to a low voltage state.
Transmission Charge Filter Bypass Switch
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| Illustration 12 | g03320660 |
The transmission charge filter bypass switch is a pressure switch. The switch alerts the ECM when the transmission charge filter is being bypassed. The contact floats to a high voltage when the switch is not closed. When the switch closes, the contact is pulled to a low or ground voltage state by the return line.
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| Illustration 13 | g03425566 |
The engine retarding lever acts a four position switch that controls the amount of engine retarding. There are three ECM contacts that are normally open, these contacts are closed and pulled to a low voltage state depending on the position of the lever.
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| Illustration 14 | g03425600 |
The differential lock switch is a single pole switch. The switch is normally open and the ECM contact floats to a high-voltage state. When the switch is activated, the ECM contact is pulled to a low voltage state and the ECM detects an operator request to lock the differential.
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| Illustration 15 | g03886287 |
The transmission hold switch is a single pole switch located in the joystick. The switch has a normally open contact and a normally closed contact. When the switch is activated, the normally open contact closes and the normally closed contact opens. The ECM normally open contact is pulled to a low voltage state and the normally closed contact floats to a high-voltage state. The change in voltage state causes the ECM to hold the current transmission gear.
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| Illustration 16 | g03425512 |
The differential lock solenoid is an on/off type solenoid. The ECM energizes the solenoid based on operator request. When the solenoid is energized, the differential is locked.
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| Illustration 17 | g03319894 |
Each of these solenoid valves is designed to control the flow of to a clutch plate. When the solenoid is not engaged or receiving a low duty cycle signal, the solenoid does not allow power train hydraulic oil to engage a clutch plate. As the duty cycle of the signal to the solenoid increases, the solenoid allows some flow and the clutch begins to engage. When the duty cycle of the signal to the solenoid is at the maximum, the flow of power train hydraulic oil fully engages the clutch. The engagement of a clutch is proportional to the duty cycle of the signal sent by the ECM.
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.
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.