Switches
Switches provide information to the ECU. Switches are two state devices. The switches are either open or the switches are closed.
Closed - The switch closes the circuit to ground or the switch closes the circuit to the battery.
Open - the switch opens a circuit to the ECU input.
Note: Damage to the wiring harness can create an open circuit. The ECM cannot distinguish between a damaged circuit and an open circuit. The ECM will read an open circuit for a switch to ground if the wiring harness has been damaged. A diagnostic code may not be initiated. A switch with this type of failure does not change state when the switch is toggled. The following three switches may have this type of failure:
- Keyswitch
- Shifter Select Switch
- 2WD/AWD Switch
- Alternate max gear for the primary shifter
- Alternate max gear for the secondary shifter
- PTO no. 1 and PTO no. 2 enable
- PTO no. 1 and PTO no. 2 increment/decrement
- Quick to neutral
Key Start Switch
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| Illustration 1 | g00927534 |
When the key start switch is in the ON position, electrical power from the batteries is supplied to the electronic control modules.
When the key start switch is in the START position and the conditions for starting the engine are satisfied, the start relay is energized.
Oil Filter Bypass Pressure Switch
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| Illustration 2 | g01252539 |
The pressure switch has a plunger inside the switch that closes the contacts with an acceptable pressure drop across the screen. The pressure switch grounds the signal circuit during normal operation. The pressure switch plunger moves in order to allow the pressure switch contacts to open. The pressure switch contacts open when pressure across the screen is greater than the specified value. If the screen is restricted the open pressure switch sends a signal to the ECU. The ECU informs the operator that the screen is restricted or dirty. The normal state of a pressure switch that is not installed is normally open. With a PSI below 49 PSI, the switch will remain closed. When the PSI is at 50 PSI as a minimum, the switch will open. The circuit for the switch is normally open. The bypass valve will open in order to protect the system if the filter is restricted. The bypass switch provides an input signal to the ECU. The ECU determines if the filter is restricted and the ECU informs the Caterpillar Electronic Technician.
Note: The circuit for this switch is in series with the lube oil filter pressure switch.
Lube Oil Filter Bypass Pressure Switch
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| Illustration 3 | g01315607 |
The pressure switch has a plunger inside the switch that closes the contacts with an acceptable pressure drop across the screen. The pressure switch grounds the signal circuit during normal operation. The pressure switch plunger moves in order to allow the pressure switch contacts to open. The pressure switch contacts open when pressure across the screen is greater than the specified value. If the screen is restricted the open pressure switch sends a signal to the ECU. The ECU informs the operator that the screen is restricted or dirty. The normal state of a pressure switch that is not installed is normally open. With a PSI below 49 PSI, the switch will remain closed. When the PSI is at 50 PSI as a minimum, the switch will open. The circuit for the switch is normally open. The bypass valve will open in order to protect the system if the filter is restricted. The bypass switch provides an input signal to the ECU. The ECU determines if the filter is restricted and the ECU informs the Caterpillar Electronic Technician.
Note: The circuit for this switch is in series with the transmission oil filter pressure switch.
Shifter Select Switch
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| Illustration 4 | g01251358 |
The OEM transmission uses a shift pad. The shift pad is a J1939 shifter. The shift pad uses a J1939 signal to ECU. The software needs the ability to program which type of shifter that is connected as the primary shift selector input. The ability to have two shift selectors is desired for some applications. This function requires a SWG input and some programmable parameters. The secondary shift selector input is also a J1939 shifter. When the shift selector input is grounded, then the shifter input switches to the second shifter. The switch will only occur if both shifters are selecting Neutral, the transmission is in Neutral, and the output speed is zero. The display of the inactive shifter should be blank if it is a Push Button shift pad. If any of the conditions are not met, then the shifter input will not switch until all the conditions are met.
There is a programmable maximum gear limit and a programmable alternate maximum gear limit for each shifter.
| Primary Shift Selector Input | ||
| On/Off | Type | Signal |
| Off (default) | Data Link Shifter | J1939 |
| Secondary Shift Selector Input | ||
| On/Off | Type | Signal |
| Off (default) | Data Link Shifter | J1939 |
Park Brake Pressure Switch
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| Illustration 5 | g01952857 |
The switch is normally closed to ground, meaning that the park brake is released. When the switch is open, the park brake is engaged. The park brake pressure switch is used to determine the park brake has been applied. When this input indicates the park brake has been applied, the ECU will shift into first gear but will not upshift higher than first unless the engine is oversped. The logic assumes a park brake system that is spring applied and requires hydraulic pressure to release the park brake. Typically, a pressure switch is used with a trip point high enough to ensure the park brake is completely released. However, if the OEM vehicle has air brakes, a pressure switch suitable for the air system could be used.
Service Brake Pressure Switch
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| Illustration 6 | g01251321 |
The switch is normally open, meaning that the service brake is released. When the switch is closed to ground, the service brake is engaged. The service brake pressure switch is used to determine when the driver is applying the brakes. The ECU will use elevated shift points, which will run the transmission in a lower gear to improve the effects of engine braking. Typically this is a pressure switch in the brake hydraulics with a relatively low trip point, similar to a sensor which activates brake lights. However, if the OEM vehicle has air brakes, a pressure switch suitable for the air system could be used. Another alternative is a limit switch mounted on the brake pedal.
Primary and Secondary Gear Shifter Switch
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| Illustration 7 | g01251378 |
The shifter inputs are used by the ECU to read the desired gear from on or both keypad shifters.
Note: In order to properly switch from on shifter to the other, both shifters must be in neutral, then toggling the selector switch will signal the ECU to switch from on shifter to the other. This selector switch is not required for single shifter pump applications and the single shift pad should be wired as the primary shifter.
Well Service Work-over Rig Operation
The ECU will use the state of the selector switch to determine which shifter is active and will ignore the other shifter. The ECU will also run a different shift schedule based on the active shifter. The shifter in the cab must be configured by location code wiring to be the primary shifter. For the shifter in the cab, the ECU will automatically shift the transmission up and down based on output speed. The shifter on the deck must be configured by location code wiring to be the secondary shifter. For the shifter on the deck, the ECU will function in a power shift mode, shifting into the gear that is selected. The ECU will not shift into reverse when using the deck shifter. The shifter will display two alpha-numeric codes. The display on the left is the desired gear and the display on the right is the actual gear. Both shifters will display the information for the shifter that is active. For example if the vehicle is in Road Mode, the deck shifter will display the information about the cab shifter.
Pump Operation
If the optional second shifter is used, the ECU will use the state of the selector switch to determine which shifter is active and will ignore the other shifter. The ECU will run the same shift schedule for both shifters, a power-shift mode, shifting into the gear that is selected. The ECU will not shift into reverse. The shifter will display two alpha-numeric codes. The display on the left is the desired gear and the display on the right is the actual gear. If the optional second shifter is used, both shifters will display the information for the shifter that is active. If "R" is selected the transmission will engage a combination of clutches. The clutches will act as a park gear and lock the output of the transmission.
Sensors
Speed Sensors
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| Illustration 8 | g01252540 |
The transmission is equipped with the following speed sensors:
- Engine Speed Sensor
- Torque Converter Output Speed Sensor
- Transmission Output Speed Sensor
- Work Mode Disconnect Output Speed Sensor
- Rear Wheel Drive Disconnect Speed Sensor
- Front Wheel Drive Disconnect Speed Sensor
As the gear teeth pass the end of each sensor, an AC voltage is produced. The frequency of the voltage is proportional to the speed of the gear teeth. The ECU uses these signals to make decisions.
Transmission Oil Temperature Sensor
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| Illustration 9 | g01297197 |
The hydraulic oil temperature sensor monitors the temperature of the hydraulic oil. The high hydraulic oil temperature indicator will be supported by an input into the ECU. This will result in the indicator being turned on and a level 2 event being logged whenever the temperature sensor reaches 100°C by the ECU providing a ground signal to the input on the LED panel.
Position Sensor
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| Illustration 10 | g01297198 |
Each disconnect has a position sensor that is mounted in it. The sensor is used in order to determine the engagement of the disconnect. The position thresholds are preset. If a disconnects position is beyond the "fully engaged" threshold, then that disconnect is considered to be "engaged". If a disconnects position is beyond the "fully disengaged" threshold, then that disconnect is considered to be "disengaged".
Work Mode Fork
The position sensor connects to the ECU at connector contact J2-22, J2-33, J1-48. The 8 volt supply to the sensor connects to the ECU at J1-48. The sensor's signal to the ECU connects at connector contact J2-33. The sensor connects to ground at the ECU at connector contact J2-22.
Front Wheel Drive Fork
The position sensor connects to the ECU at connector contact J2-22, J2-32, J1-48. The 8 volt supply to the sensor connects to the ECU at J1-48. The sensor's signal to the ECU connects at connector contact J2-32. The sensor connects to ground at the ECU at connector contact J2-22.
Rear Wheel Drive Fork
The position sensor connects to the ECU at connector contact J2-22, J2-26, J1-48. The 8 volt supply to the sensor connects to the ECU at J1-48. The sensor's signal to the ECU connects at connector contact J2-26. The sensor connects to ground at the ECU at connector contact J2-22.