C7 and C9 Industrial Engines Troubleshooting – Power Take-Off – Test

Use this procedure to troubleshoot any suspect problems with the circuits for the power take-off controls (PTO). 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 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.


Illustration 1 g01121879
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 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.


Illustration 2 g01105373
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 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. After the desired engine speed has been 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. After the desired engine speed has been 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.


Illustration 3 g01120532
Left side view

(1) P61 customer connector

(1) J1/P1 ECM connectors


Illustration 4 g01102468
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


Illustration 5 g01123458
J61/P61 terminals that are associated with the PTO

(19) Input from the PTO interrupt switch

(29) Input from the PTO enable switch

(30) Input from the PTO ramp up switch or set switch

(39) Input for PTO ramp down switch or resume switch

Table 1
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring

A. Turn the keyswitch to the OFF position.

B. Thoroughly inspect connectors (1) and (2). Refer to Troubleshooting, “Electrical Connectors – Inspect”.

C. Perform a
45 N (10 lb) pull test on each of the wires that are associated with the circuits for the PTO switches.

D. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect” for the correct torque values.

E. Check the allen head screw on the customer connector for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect” for the correct torque value.

F. Check the harness and wiring for abrasions and for pinch points from the battery to the ECM.

Electrical Connectors and Wiring Results: The connectors and wiring are OK. If the engine is equipped with a customer connector, proceed to Test Step 2. Otherwise, proceed to Test Step 3.

Results: There is a problem with the connectors and/or the wiring.

Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.

STOP

2. Check the Inputs from the Switches at the J61 Customer Connector

A. Disconnect the J61 connector.

B. Refer to Table 2. Connect a voltage test lamp between the input for the suspect switch circuit and terminal J61-31 (+Battery).

C. Observe the voltage test lamp as you operate the suspect switch.

Inputs Results: The voltage test lamp turns on when the switch is closed. The voltage test lamp turns off when the switch is opened. The circuit is operating correctly. Connect the J61 connector. Proceed to Test Step 3.

Results: The voltage test lamp does not turn on when the switch is closed. Alternatively, the voltage test lamp does not turn off 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 completely coupled. Verify that the repair eliminates the problem.

STOP

Table 2
J61 Terminals for the Inputs from the PTO Switches
Switch J61 Terminals
PTO enable switch 29
PTO ramp up switch or set switch 58
PTO ramp down switch or resume switch 60
PTO interrupt switch 41
Table 3
Troubleshooting Test Steps Values Results
3. Check the Inputs from the Switches at the J1 Connector

A. Disconnect the P1 connector.

B. Refer to Table 4. Connect a voltage test lamp between the input for the suspect switch circuit and terminal J1-48 (+Battery).

C. Observe the voltage test lamp as you operate the suspect switch.

Inputs Results: The voltage test lamp turns ON when the switch is closed. The voltage test lamp turns OFF when the switch is opened. The switch circuit is operating correctly. The problem may be in the ECM.

Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the problem is not resolved, temporarily install a new ECM. Refer to Troubleshooting, “Replacing the ECM”.

If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. IF the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM.

STOP

Results: The voltage test lamp does not turn on when the switch is closed. Alternatively, the voltage test lamp does not turn off 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.

STOP

Table 4
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

 

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