Use this procedure to troubleshoot any suspect problems with the circuits for the Power Take-Off (PTO) controls . The PTO controls provide an alternative method of controlling the desired engine speed.
The Electronic Control Module (ECM) provides the PTO speed control function. The PTO speed control function requires the following inputs:
- PTO switches
- The "PTO Mode" parameter
The PTO switches enable the PTO speed control function and the PTO switches to control the desired engine speed.
The "PTO Mode" parameter determines the mode of operation. There are two modes of operation: "Ramp Up/Ramp Down" and "Set/Resume". Use the Caterpillar Electronic Technician (ET) in order to change the value of the parameter.
"Ramp Up/Ramp Down" Mode
This mode uses three inputs. The inputs are provided by two switches. Refer to Illustration 1.
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| Illustration 1 | g02102909 |
Schematic for the PTO inputs for the "Ramp Up/Ramp Down" mode of operation | |
Placing the PTO enable switch to the Enable position transfers the control of the desired engine speed. The control is transferred from the throttle position sensor to the PTO speed control function. The PTO ramp up/down switch controls the desired engine speed.
The PTO ramp up/down switch is spring loaded to the normally open position. When the switch is held in the Ramp Up position, the desired engine speed increases according to the value of the "Engine Accel Rate" parameter. When the switch is released, the desired engine speed maintains the set speed. After the desired engine speed has been set, momentarily placing the switch in the Ramp Up position increases the desired engine speed by 20 RPM.
When the PTO ramp up/down switch is held in the Ramp Down position, the desired engine speed decreases according to the value of the "Engine Accel Rate" parameter. When the switch is released, the desired engine speed maintains the set speed. After the desired engine speed has been set, momentarily placing the switch in the Ramp Down position decreases the desired engine speed by 20 RPM.
If the "PTO Ramp Up" and "PTO Ramp Down" inputs are connected to the -Battery at the same time, the ECM will ignore the inputs. The desired engine speed will not change.
"Set/Resume" Mode
This mode uses four inputs. The inputs are provided by three switches. Refer to Illustration 2.
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| Illustration 2 | g02102912 |
Schematic for the PTO inputs for the "Set/Resume" mode of operation | |
Placing the PTO enable switch to the Enable position transfers the control of the desired engine speed. The control is transferred from the throttle position sensor to the PTO speed control function. The PTO interrupt switch momentarily transfers control back to the throttle position sensor. The PTO set/resume switch controls the desired engine speed.
The PTO set/resume switch is spring loaded to the normally open position. If the switch is momentarily placed in the Set position, the desired engine speed will be set to the current engine speed. If the switch is held in the Set position, the desired engine speed will increase according to the value of the "Engine Accel Rate" parameter. Once set, the desired engine speed will increase by 20 RPM when the PTO ramp up/down switch is momentarily placed in the Set position.
If the PTO set/resume switch is momentarily placed in the Resume position, the desired engine speed will be set to the current engine speed. If the switch is held in the Resume position, the desired engine speed will decrease according to the value of the "Engine Accel Rate" parameter. Once set, the desired engine speed will decrease by 20 RPM when the switch is momentarily placed in the Resume position.
If the "PTO Set" and "PTO Resume" inputs are connected to the -Battery at the same time, the ECM will ignore the inputs. The desired engine speed will not change.
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| Illustration 3 | g01383146 |
P1 terminals that are associated with the PTO (P1-41) Input from the PTO interrupt switch (P1-56) Input from the PTO enable switch (P1-58) Input from the PTO ramp up switch or set switch (P1-60) Input for PTO ramp down switch or resume switch | |
| Troubleshooting Test Steps | Values | Results |
|---|---|---|
1. Check the Inputs from the Switches at the Customer Connector A. Disconnect the customer connector. B. Refer to Table 2. Connect a voltage test lamp between the input for the suspect switch circuit and the appropriate terminal on the customer connector. C. Observe the voltage test lamp as you operate the suspect switch. |
Switch Inputs |
Result: The voltage test lamp illuminates when the switch is closed. The voltage test lamp does not illuminate when the switch is opened. The circuit is operating correctly. Connect the customer connector. Proceed to Test Step 2. Result: The voltage test lamp does not illuminate when the switch is closed. Alternatively, the voltage test lamp stays illuminated when the switch is opened. There is a problem with the suspect switch and/or the wiring. Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. Verify that the repair eliminates the problem. |
2. Check the Inputs from the Switches at the J1 ECM Connector A. Disconnect the P1 connector. B. Refer to Table 3. Connect a voltage test lamp between the input for the suspect switch circuit and terminal J1-48. C. Observe the voltage test lamp as you operate the suspect switch. |
Switch Inputs |
Result: The voltage test lamp illuminates when the switch is closed. The voltage test lamp does not illuminate when the switch is opened. There may be an intermittent problem in the circuit. Repair: Clean the connector, if necessary. Repair the wiring and/or the connector. Replace parts, if necessary. Verify that the connection is secure. Verify that the repair eliminates the problem. Result: The voltage test lamp does not illuminate when the switch is closed. Alternatively, the voltage test lamp stays illuminated when the switch is opened. There is a problem in the wiring between the J1 connector and the switch. There may be a problem in a connector. Repair: Repair the wiring and/or the connector. Replace parts, if necessary. Verify that the repair eliminates the problem. |
| Customer Connector Terminals for the Inputs from the PTO Switches | |
| Switch | Customer Connector Terminals |
| PTO enable switch | 29 |
| PTO ramp up switch or set switch | 30 |
| PTO ramp down switch or resume switch | 39 |
| PTO interrupt switch | 19 |
| J1 Terminals for the Inputs from the PTO Switches | |
| Switch | J1 Terminals |
| PTO Enable Switch | 56 |
| PTO Ramp Up Switch or Set Switch | 58 |
| PTO Ramp Down Switch or Resume Switch | 60 |
| PTO Interrupt Switch | 41 |
Test Step 1.
Results:
- The procedure corrected the issue. - STOP
- The procedure did not correct the issue. -
Repair: Contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).
STOP