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| Illustration 1 | g03307257 |
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| Illustration 2 | g01309473 |
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ECM Connectors and Contacts | |
The Transmission / Chassis ECM determines actions that are based on input information and memory information. After the Transmission / Chassis ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the Transmission / 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 CAN network.
Note: The ECM is not serviceable. 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.
| Transmission / Chassis ECM Contact Description J1 Contact Descriptions(1) | ||
|---|---|---|
| No.(2) | Type | Function |
| 2 | Differential Speed Input + | Transmission Input Speed Sensor + |
| 3 | Differential Speed Input - | Transmission Input Speed Sensor - |
| 4 | Differential Speed Input + | Intermediate Speed Sensor 1 + |
| 5 | Differential Speed Input - | Intermediate Speed Sensor 1 - |
| 6 | Differential Speed Input + | Intermediate Speed Sensor 2+ |
| 7 | Differential Speed Input - | Intermediate Speed Sensor 2- |
| 8 | Differential Speed Input + | Transmission Speed Sensor 4 + |
| 9 | Differential Speed Input - | Transmission Speed Sensor 4 - |
| 10 | CAN Data Link - | CAN C Data Link - |
| 11 | Sensor Power Output | 5V Sensor Supply |
| 12 | Sourcing Driver Output | Park Brake Solenoid |
| 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 | CAN Data Link + | CAN C Data Link + |
| 22 | Analog Input | Transmission Oil Temperature Sensor |
| 23 | Battery Return | Battery - |
| 26 | Switch to Ground Input | ECM Location 0 |
| 31 | Battery Power Input | Battery + |
| 32 | Switch to Ground Input | ECM Location Enable |
| 33 | Switch to Ground Input | Transmission Filter Bypass Switch |
| 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 |
| 46 | Battery Power Input | Battery + |
| 47 | Battery Power Input | Battery + |
| 48 | Sourcing Driver Output | Transmission Solenoid 7 |
| 49 | Sourcing Driver Output | Transmission Solenoid 2 |
| 50 | Sourcing Driver Return | PWM Drivers 1 - 4 Return |
| 51 | Sourcing Driver Output | Transmission Solenoid 3 |
| 52 | Sourcing Driver Output | Transmission Solenoid 4 |
| 55 | Sourcing Driver Return | PWM Driver 9-10 Return |
| 56 | Sensor Power Return | 10V Sensor Return |
| 57 | Battery Return | Battery - |
| 58 | Sourcing Driver Output | Transmission Solenoid 5 |
| 60 | Sourcing Driver Return | PWM Driver 5-8 Return |
| 61 | Sourcing Driver Output | Transmission Solenoid 1 |
| 62 | Sourcing Driver Output | Transmission Solenoid 8 |
| 65 | Sourcing Driver Output | Transmission Solenoid 6 |
| 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. |
| Transmission / Chassis ECM Contact Description J2(1) | ||
|---|---|---|
| No.(2) | Type | Function |
| 3 | Sourcing Driver Output | Transmission Pump Bypass Solenoid |
| 4 | Sourcing Driver Return | Load Return 1 |
| 6 | Sourcing Driver Output | Differential Lock Solenoid |
| 8 | Sourcing Driver Return | Load Return 2 |
| 22 | Return | Sensor / Driver Return |
| 25 | PWM Input | Transmission Oil Pressure Sensor |
| 26 | Switch to Ground Input | Transmission Shifter Gear Sensor 1 |
| 33 | Switch to Ground Input | Transmission Shifter Gear Sensor 2 |
| 34 | Switch to Ground Input | Transmission Shifter Direction Sensor 1 |
| 35 | Switch to Ground Input | Transmission Shifter Direction Sensor 2 |
| 43 | PWM Input | Modulation Pedal Position Sensor |
| 45 | Switch to Ground Input | Modulation Pedal Switch N/C |
| 46 | Switch to Ground Input | Modulation Pedal Switch N/O |
| 47 | Switch to Ground Input | Transmission Auto/Manual N/O |
| 51 | PWM Input | Park Brake Pressure Sensor |
| 52 | Switch to Ground Input | Transmission Auto/Manual N/C |
| 53 | Switch to Ground Input | Differential Lock N/O |
| 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 - |
| (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 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.
Transmission Input Speed Sensor
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| Illustration 3 | g03319385 |
The ECM receives signals from the transmission input speed sensors as frequency signals. The transmission input speed sensors are passive sensors. The signals indicate the rotational speed of the output 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.
Transmission Intermediate Speed Sensor
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| Illustration 4 | g03319385 |
The ECM receives signals from the transmission intermediate speed sensors as frequency signals. The transmission intermediate speed sensors are passive sensors. The signals indicate the rotational speed of the output 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.
Transmission Output Speed Sensors
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| Illustration 5 | g03534910 |
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.
Transmission Oil Temperature Sensor
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| Illustration 6 | 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 7 | g03541441 |
The modulation pedal sensor is an active pulse width modulated position sensor. The duty cycle of the sensor is proportional to the position of the inching pedal. The ECM monitors this operator input to determine operator movement request.
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| Illustration 8 | g03324121 |
The parking brake pressure sensor measures the pressure of the hydraulic oil that releases the parking brake in the transmission. The sensor sends a pulse width modulated signal to the ECM. The duty cycle of the signal increases as pressure increases.
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.
Transmission Filter Bypass Switch
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| Illustration 9 | g03534958 |
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 10 | g03543004 |
The modulation pedal switch is a single pole switch. The switch has a normally open contact and a normally closed contact. In the normally operating position, the normally open contact floats to a high-voltage state and the normally closed contact is pulled to a low voltage state. The last ECM contact is an extra normally closed contact. When the switch is activated the normally closed contacts float to a high-voltage state, and the normally open contact is pulled to a low voltage state. By monitoring the voltage state of the three ECM contacts, the ECM is able to determine if the modulation pedal switch has been engaged.
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| Illustration 11 | g06357272 |
When the autoshift switch is pressed, a signal is sent through the SAE J1939 (CAN) Data Link to the Transmission / Chassis ECM. The ECM is able to determine the operator request for transmission shift control.
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 12 | g03535137 |
The parking brake solenoid is an on/off type solenoid. The ECM energizes the solenoid when the parking brakes are to be released. The parking brake is spring applied, and when the parking brake solenoid is energized, transmission hydraulic oil is allowed to release the braking brake.
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| Illustration 13 | g03535518 |
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.
Transmission Pump Bypass Solenoid
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| Illustration 14 | g03425512 |
The transmission pump bypass solenoid is an on/off type solenoid. The ECM energizes the solenoid based on transmission oil temperature. When the solenoid is energized, the pumps are bypassed.
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| Illustration 15 | g03535025 |
Each of these solenoid valves is designed to control the flow of power train oil 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 Transmission / 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 has one type of data link system.
- 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.
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.