Power Take-Off: Description and Operation
Power Take-Off Fast Idle System Description
A power take off (PTO) is a mechanical device used in order to transmit power from the vehicle powertrain to a mechanical or hydraulic device that has been installed by an aftermarket upfitter. The PTO Fast Idle System (if equipped) provides an electronic means of increasing the engine idle speed in order to operate the PTO driven device at the proper operating speed.
Using a scan tool, the PTO Fast Idle System can be programmed to operate in one of the following modes:
* The Stationary Preset Mode
* The Stationary Variable Mode
* The Mobile Variable Mode
If the vehicle is equipped with cruise control, the PTO Fast Idle System is controlled by the following switches:
* The PTO ENABLE switch
* The CRUISE ON/OFF switch
* The SET/COAST switch
* The Resume/Accel (R/A) switch
If the vehicle is not equipped with cruise control, the PTO Fast Idle System is controlled by the following switches:
* The PTO ENABLE switch
* The PTO ON/OFF switch
* The PTO UP switch
* The PTO SET/DOWN switch
When the PTO Fast Idle System is engaged, the engine speed is controlled by the inputs from the cruise control switches (ON/OFF, SET/COAST, RESUME/ACCEL) or the PTO Fast Idle control switches (PTO ON/OFF, SET/DOWN, RESUME/UP) to the Throttle Actuator Control (TAC) module. If the engine load varies, the TAC module controls the throttle blade to the appropriate position in order to maintain the desired engine speed. The engine speeds are determined by the PTO Options and the Fast Idle Speed values that have been selected on the scan tool.
Conditions for Engaging the PTO Fast Idle System
Important: The PCM must receive a brake APPLIED and RELEASED signal or a clutch DEPRESSED and RELEASED signal during the current ignition cycle in order to engage the Stationary Preset or the Stationary Variable Modes of the PTO Fast Idle System.
Stationary Preset Mode
1. The engine is running
2. The transmission is in Park (P) or Neutral (N)
3. A vehicle speed is not detected
4. The brakes have been applied and released or the clutch pedal has been depressed during the current ignition cycle
5. The cruise control (PTO) ON/OFF switch is in the ON position
6. The PTO ENABLE switch is in the ON position
When the conditions are met in the above order, the engine speed will increase to the Base Fast Idle value that has been selected using the scan tool.
When the conditions are met in the following order, the engine speed will not change until the SET/COAST (SET/ DOWN) or the RESUME/ACCEL (PTO RESUME/UP) switches are depressed:
1. The engine is running
2. The transmission is in Park (P) or Neutral (N)
3. A vehicle speed is not detected
4. The brakes have been applied and released or the clutch pedal has been depressed during the current ignition cycle
5. The PTO ENABLE switch is in the ON position
6. The Cruise Control (PTO) ON/OFF switch is in the ON position
Stationary Variable Mode
1. The engine is running
2. The transmission is in Park (P) or Neutral (N)
3. A vehicle speed is not detected
4. The brakes have been applied and released or the clutch pedal has been depressed during the current ignition cycle
5. The cruise control (PTO) ON/OFF switch is in the ON position
6. The PTO ENABLE switch is in the ON position
When the above conditions are met in the above order, the engine speed will increase to the Base Fast Idle value that has been selected using the scan tool. The engine speed can then be decreased and increased, in 25 RPM increments, by using the SET/COAST (SET/ DOWN) and the RESUME/ACCEL (RESUME/ UP) switches.
When the conditions are met in the following order the engine speed can be increased, using the accelerator pedal, to any desired speed that is below the selected Maximum Fast Idle Speed. The engine speed can then be maintained by momentarily depressing the SET/PTO DOWN switch. The engine speed can then be decreased and increased, in 25 RPM increments, by using the SET/COAST (RESUME/DOWN) and the RESUME/ACCEL (RESUME/UP) switches:
1. The engine is running
2. The transmission is in Park (P) or Neutral (N)
3. A vehicle speed is not detected
4. The brakes have been applied and released or the clutch pedal has been depressed during the current ignition cycle
5. The PTO ENABLE switch is in the ON position
6. The cruise control (PTO) ON/OFF switch is in the ON position
Mobile Variable Mode
1. The engine is running
2. The transmission is not in Park (P) or Neutral (N)
3. The PTO ENABLE switch is in the ON position
4. The cruise control (PTO) ON/OFF switch is in the ON position
5. The engine speed is more than the Base Fast Idle Speed that has been selected using the scan tool
6. The engine speed is less than the Maximum Fast Idle Speed that has been selected using the scan tool
7. The vehicle speed is more than 5 kp/h (3 MPH)
8. The vehicle speed is less than the Maximum Vehicle Speed that has been selected using the scan tool
When the conditions are met in the following order the engine speed can be increased, using the accelerator pedal, to any desired speed that is below the selected Maximum Fast Idle Speed. The engine speed can then be maintained by momentarily depressing the SET/COAST (SET/DOWN) switch. The engine speed can then be decreased, in 25 RPM increments down to the Base Fast Idle Speed by using the SET/COAST (SET/DOWN) switch. The engine speed can be increased, in 25 RPM increments, by using the RESUME/ACCEL (RESUME/UP) switch.
Conditions for Disengaging the PTO Fast Idle System
Stationary Preset Mode
* The PTO ENABLE switch is turned to the OFF position
* The cruise (PTO) ON/OFF switch is turned to OFF position
* The engine is not running
* The clutch pedal is depressed
* The brakes are applied
* The transmission is not in Park (P) or Neutral (N)
* A vehicle speed is being detected
* The engine speed is above the selected Maximum Fast Idle Speed value
Stationary Variable Mode
* The PTO ENABLE switch is turned to the OFF position
* The cruise (PTO) ON/OFF switch is turned to OFF position
* The engine is not running
* The clutch pedal is depressed
* The brakes are applied
* The transmission is not in Park (P) or Neutral (N)
* A vehicle speed is being detected
* The engine speed is above the selected Maximum Fast Idle Speed value
Mobile Variable Mode
* The PTO ENABLE switch is turned to the OFF position
* The Cruise (PTO) ON/OFF switch is turned to OFF position
* The engine is not running
* The clutch pedal is depressed
* The brakes are applied
* The transmission is in Park (P) or Neutral (N)
* A vehicle speed less than 5 kph (3 MPH) is being detected
* The engine speed is above the selected Maximum Fast Idle Speed value
* A vehicle speed greater than the selected Maximum Vehicle Speed is detected
When certain conditions cause the Mobile Variable Mode to disengage, pressing the RESUME/ACCEL (RESUME/UP) switch will return the engine speed to the last set speed.