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
