Introduction
The electro-hydraulic (EH) steering system is standard on the 980M and 982M machines. The Implement Electronic Control Module (ECM) and the Power Train ECM work together to provide a primary steering system and a secondary steering system.
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| Illustration 1 | g03556936 |
Components that are used for the electronic control of the primary steering system and the secondary steering system (1) Implement ECM (2) Power train ECM (10) Left Armrest Switch (11) Steering Control Spool Position Sensor (12) Steering Pump Pressure Sensor (if equipped) (13) Secondary Steering Pump Pressure Sensor (if equipped) (14) Steering Pilot Solenoid (15) Left and Right Primary Steering Solenoids (16) Feedback Motor Control (17) Steering Control Lever (18) Steering Cylinder Position Sensors (19) Operator Present (20) Left and Right Secondary Steering Solenoids (21) Secondary Steering Pump Relay (22) Data Links | |
The machines are equipped with an electro-hydraulically controlled steering system. The implement ECM (1) and the power train ECM (2) work together to provide a primary and secondary steering system.
The Implement ECM and Power Train ECM communicate over the data links (22) . The ECMs use the CAN A Data Link or CAN B Data Link as the primary data links. In the case of a failure, the ECMs will use the Cat Data Link as a backup.
Both ECMs monitor the steering control lever (17) (steering position sensors). The ECMs (both) also monitor steering cylinder position sensors (18) , and if the operator is present (19) . These inputs are used for steering (articulating) the machine when either the primary steering system is active or when the secondary steering system is active.
The Implement ECM also monitors the left armrest switch (10) and the steering control spool position sensor (11) . The ECM uses the steering control spool position sensor, along with the steering cylinder position sensors, to ensure the machine articulates in the desired direction. The steering pump pressure sensor (12) and secondary steering pump pressure sensors (13) also provide input to the Implement ECM for the secondary steering pump.
The Implement ECM sends current to the steering pilot solenoid (14) and to the left and right primary steering solenoids (15) . The primary steering solenoids are used to articulate the machine. The Implement ECM also controls the feedback motor (16) in the base of the left-hand steering control. The feedback motor provides feedback (resistance) to the operator as the machine is articulated.
The Power Train ECM sends current to the left and right secondary steering solenoids (20) to articulate the machine if either of the primary steering solenoids has an active fault code. The Power Train ECM also energizes the secondary steering pump relay (21) if the steering pump or engine fails while the machine is moving.
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| Illustration 2 | g03557589 |
Steering Control Lever (3) Left Hand Steering Control (23) Speed range thumb roller (24) Transmission direction switch | |
The EH steering system is equipped with a steering control lever (3) . The steering control lever combines the steering functions and the transmission functions for the machine. Move the control to the left or to the right to articulate the machine.
The transmission direction switch (24) is located on the front of the control. The transmission direction switch allows the operator to choose the machine direction. The speed range thumb roller (23) is located near the top of the steering control lever. The thumb roller allows the operator to select the transmission speed.
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| Illustration 3 | g03877426 |
Steering Control Lever Connections | |
The steering function uses hall cell type sensors that send PWM signals to the Implement ECM and to the Power Train ECM. This image shows the electrical connections between the steering control lever, the Implement ECM, and the Power Train ECM.
The steering control lever contains three steering sensors that are necessary for correct steering operation. All three sensors send a PWM signal to both the Implement ECM and the Power Train ECM. Steering sensors 1 and 2 are powered from the Implement ECM. Steering sensor 3 is powered from the Power Train ECM.
A Level 3 Warning occurs when any steering lever position sensor fails. The machine will continue to articulate normally (with an active Level 3 warning) using the two remaining sensors.
The steering control lever also contains the feedback motor. The feedback motor aligns the control with the machine articulation angle if all of the conditions have been met. The feedback motor also provides feedback (resistance) to the operator when the operator articulates the machine.
4
The Implement ECM compares the position of the steering control lever to the machine articulation angle. The amount of resistance the feedback motor produces is determined by the difference between the machine articulation angle and the steering control lever position. The larger the difference between the machine articulation angle and the steering control lever position, the greater the resistance will be.
If the steering control lever is released in the desired position when there is resistance, the steering control lever will move in the direction of the resistance until the control aligns with the articulation angle of the machine. If the steering control lever is released in a desired position when there is no resistance, the steering control lever will remain in that position.
A Level 3 Warning occurs when the feedback motor has a fault code or is not responding to the commands from the Implement ECM. The machine will continue to articulate normally (with an active Level 3 warning), but the operator will not receive feedback from the steering control lever.
There are some points to consider when diagnosing Failure Mode Indicators (FMI) for the steering lever position sensors:
- Verify that 8 V power supply for the Implement ECM does not have any active codes. Correct any problems with the 8 V power supply if any diagnostic codes are active.
- Verify that 8 V power supply for the Power Train ECM does not have any active codes. Correct any problems with the 8 V power supply if any diagnostic codes are active.
- The Implement ECM and the Power Train ECM receive an input signal from the steering position sensors. Both ECMs can activate a diagnostic code for all three sensors. Most likely the sensor is operating correctly if one ECM has activated a diagnostic code and the other ECM has not. When this situation occurs, a poor connection in the machine harness would be suspected. When both ECMs have activated the diagnostic code, either the sensor or a harness problem could be the cause. That both ECMs have failed when both ECMs have activated the diagnostic code is unlikely.
Electronic Control Modules ECMs
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| Illustration 4 | g03032197 |
(1) Connector view from ECM side (2) Connector view from harness side | |
The ECM bases decisions 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).
In most instances when a diagnostic code or an event code is activated, the ECM is the least likely cause of the problem. When a failure of an ECM is suspected, always ensure that the latest software is flashed on the ECM. Verify that the ECM connections are secure. Then, verify that the problem is still active before replacing an ECM
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.
Implement ECM Pin Locations
| Implement ECM Connector J1 Contact Descriptions (1) | ||
|---|---|---|
| No. | Type | Function |
| 1 | Key Switch Input | Key Switch On |
| 10 | Cat Data Link (+) | Data Link |
| 20 | Cat Data Link (-) | Data Link |
| 21 | Sensor Power Return | 5 V Return |
| 22 | Analog Input | Operator Present |
| 32 | Switch to Ground Input | Location Code Enable (Grounded) |
| 37 | Analog Input | Steering Valve Spool Position Sensor |
| 41 | Switch to Ground Input | Armrest Position Sensor Switch (N/O) |
| 42 | Switch to Ground Input | Armrest Position Sensor Switch (N/C) |
| 44 | Sensor Power Output | 8 V Sensor Power |
| 45 | Sensor Power Return | 8 V Sensor Return |
| 54 | Sourcing Driver Return | Primary Steering Left/ Right |
| 67 | Sourcing Driver Output | Left Primary Steering Solenoid |
| 68 | Sourcing Driver Output | Right Primary Steering Solenoid |
| ( 1 ) | System-specific pin locations |
| Implement ECM Connector J2 Contact Descriptions (1) | ||
| No. | Type | Function |
| 1 | Switch to Battery Input/Sourcing Driver Enable | Battery In |
| 2 | Sourcing Driver Output | Primary Steering Power Supply |
| 3 | Sourcing Driver Output | Force Feedback Motor Enable |
| 4 | Sourcing Driver Return | Driver Return |
| 15 | PWM Input | Left Steering Cylinder Position Sensor |
| 16 | PWM Input | Right Steering Cylinder Position Sensor |
| 19 | Sinking Driver Output | Secondary Steering Request Output |
| 21 | Sinking Driver Output | Force Feedback Desired Torque |
| 32 | PWM Input | Steering Lever Position Sensor 1 |
| 34 | PWM Input | Steering Lever Position Sensor 3 |
| 35 | PWM Input | Force Feedback Motor Current |
| 43 | PWM Input | Steering Pump Oil Pressure Sensor 2 |
| 48 | PWM Input | Steering Lever Position Sensor 2 |
| 51 | PWM Input | Steering Pump Sensor 1 |
Power Train ECM Pin Locations
| Power train ECM Connector J1 Contact Descriptions (1) | ||
|---|---|---|
| No. | Type | Function |
| 1 | Key Switch Input | Key ON |
| 10 | Cat Data Link (+) or CAN Data Link (-) | Cat Data Link + |
| 20 | Cat Data Link (-) or CAN Data Link (+) | Cat Data Link |
| 21 | Sensor Power Return | 5V Return |
| 27 | Switch to Ground Input | Identification Code 2 |
| 31 | Battery Power to Input | Battery + |
| 32 | Switch to Ground Input | Identification Code Enable |
| 41 | Switch to Ground Input | Armrest Position Switch N/C |
| 42 | Switch to Ground Input | Armrest Position Switch N/O |
| 45 | Sensor Power Return | 8V Return |
| 54 | Sourcing Driver Output | Driver Return |
| 57 | Battery Return | Battery - |
| 67 | Sourcing Driver Output | Left Secondary Steering Solenoid |
| 68 | Sourcing Driver Output | Right Secondary Steering Solenoid |
| ( 1 ) | Contacts that are not listed are not used. |
| Power train ECM Connector J2 Contact Descriptions (1) | ||
|---|---|---|
| No. | Type | Function |
| 15 | PWM Input | Left Steer Cylinder Position Sensor |
| 16 | PWM Input | Right Steer Cylinder Position Sensor |
| 32 | PWM Input | Steering Lever Position Sensor 1 |
| 33 | PWM Input | Secondary Steering Request Input |
| 34 | PWM Input | Steering Lever Position Sensor 3 |
| 48 | PWM Input | Steering Lever Position Sensor 2 |
| ( 1 ) | Contacts that are not listed are not used. |
Inputs
The inputs describe the status of the machine systems. Two types of inputs exist. The inputs can be either a Switch type or a sensor type. Switches provide an open, a ground, or a + battery signal to the inputs of the controller. Sensors (frequency, PWM, or voltage) provide a changing signal to the sensor inputs of the controller. The inputs to ECMs are listed in Tables 1 through 4.
Temperature Sensors
Hydraulic Oil Temperature Sensor
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| Illustration 5 | g02108634 |
Hydraulic Oil Temperature Sensor | |
The temperature sensor for the hydraulic oil informs the ECM of the temperature of the hydraulic system oil.
The sensor is designed internally to change resistance based on the temperature of the hydraulic oil. The implement ECM uses a pull up resistor to receive sensor voltage and convert the voltage to a temperature reading.
Speed Sensors
Transmission Input Speed (Torque Converter)
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| Illustration 6 | g01445489 |
A passive two-wire magnetic frequency-type sensor converts mechanical motion to an AC voltage. The torque converter speed sensor measures torque converter output speed in the range of 25 to 3000 rpm. The speed sensor information is also used by the Power Train ECM to set and adjust transmission shift points.
Transmission Output Speed (2)
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| Illustration 7 | g01445492 |
A passive two-wire magnetic frequency-type sensor converts mechanical motion to an AC voltage. The torque converter output speed sensor measures torque converter output speed in the range of 25 to 3000 rpm. The speed sensor information is also used by the Power Train ECM to set and adjust transmission shift points. Transmission speed sensors may be used in pairs.
Pressure Sensors
- Implement Pump Pressure Sensor
- Implement Pump Load Sense Pressure Sensor
- Lift Cylinder Head End Pressure Sensor (If Equipped)
- Lift Cylinder Rod End Pressure Sensor (If Equipped)
- Steering Pump Oil Pressure Sensors
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| Illustration 8 | g02571841 |
The pressure sensor sends a PWM signal to the implement ECM indicating system pressure. The duty cycle of the signal will vary in proportion to the system pressure. These PWM signals are inputs to the Implement ECM.
Position Sensors
Steering Position Sensor (STIC Control)
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| Illustration 9 | g01444766 |
The sensor is designed to tell the ECM the position of the lever. The operator controls the range through left and right movements, and the sensor sends the signal to the ECM. The sensor generates a PWM signal continuously. The duty cycle of the signal varies in proportion to the position of the lever. Refer to Illustration 3 for a description of the terminals and connections to the ECMs.
Steering Spool Postion sensor
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| Illustration 10 | g03566490 |
The sensor is designed to tell the ECM the position of the steering control spool. The sensor generates an analog voltage signal.
Lock Out Switch
Keyswitch
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| Illustration 11 | g03003739 |
Key Start Switch | |
The key start switch is an input of the transmission electronic control module (ECM). The key start switch informs the transmission ECM of an attempt to start the engine. The transmission ECM then initiates the neutral start function.
During normal machine operation, the start terminal of the key start switch is open. When the key start switch is turned to the START position, the start terminal closes to the +battery. The +battery voltage is present at connector contact J2-1 of the transmission ECM. When all starting conditions are satisfied, the transmission ECM sends a +battery signal to the connector contact J2-7. The connector contact J2-7 is for the start relay that engages the starter for engine cranking.
Note: When the key start switch is in the ON position, a +battery signal is sent to connector contact J1-1. With +battery signal to connector contact J1-1 will activate the transmission ECM.
Note: After the key start switch is initially turned to the START position, the switch will not return to the START position from the ON position. The switch must be turned to the OFF position first. Then, the switch can be turned to the START position.
Outputs
The ECMs respond 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. The outputs of the ECM are listed in Tables 3 and 3.
Solenoids
Steering Solenoids
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| Illustration 12 | g03566528 |
The steering solenoids are located on the steering control valve. The solenoid functions as a proportional valve. The solenoid modulates hydraulic pressure to move the steering control spool. The ECM increases the PWM Driver to the solenoid valve and the pilot pressure at the steering control spool is increased. The ECM decreases the PWM Driver to the solenoid valve and the pilot pressure at the steering control spool is decreased.
Steering Pilot Solenoid
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| Illustration 13 | g03566530 |
The steering pilot solenoid acts as a steering pilot On/Off solenoid. When all conditions are met, the ECM sends a PWM Driver signal to the Steering Pilot Solenoid. This pilot solenoid supplies pilot pressure to the primary steering solenoids.
Data Link
Cat Data Link
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) and contact J1-20 (wire 892-BR).
- 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.
CAN Data Link
A data link is required for communication with the service tool (Cat ET) and the electronic control modules. A data link is also required for instrument clusters and other devices that use service tool (Cat ET) communications protocol. The data link is not used in order to broadcast any diagnostic information.