C 3500 HD Truck 2WD V8-8.1L VIN G (2002)
Power Take-Off: Description and Operation
PTO Components
Cruise Control Multi-Function Switch
The operation of the PTO system may be through the function control switches located on the multifunction turn signal lever. The cruise control function
control switches includes the ON/OFF, SET/COAST, and R/A. The switch assembly provides driver control of the PTO as well as the cruise control
system. The SET/COAST and R/A switches may be used to increase and decrease engine RPM in increments of 100 RPM.
PCM
The Powertrain Control Module (PCM) is the control center of the PTO system. The PCM monitors numerous engine and vehicle functions. To engage
the PTO, the PCM must see the following conditions:
^
Engine must be running
^
Transmission must be in PARK or NEUTRAL
^
Park Brake must be set for Manual Transmission Only
^
Vehicle speed must be zero
^
Brake or Clutch must not be depressed
The PCM constantly looks at the information from various sensors and other inputs, and controls the systems that affect vehicle performance. The PCM
also performs a diagnostic test on the Electronic Throttle Control system.
PTO Relay
The PTO Relay is located on the side of the underhood fuse block. The secondary side of the relay is supplied with voltage at all times through the Fog
Lamp fuse. The PTO switch controls the voltage to the primary side of the PTO relay while the PCM controls the ground.
PTO Solenoid
The solenoid is an upfitter supplied pan and is replaceable on most PTOs. The PTO solenoid is used on clutch activated PTOs. The PTO relay supplies
the solenoid with voltage when the relay is energized.
PTO Switch
The PTO Switch is mounted in the center of the Instrument Panel. The PTO Switch has three positions: OFF, ON and SET. When the PTO switch is in
ON voltage will be present on the PTO On Switch Signal circuit at the relay and the PCM. When the switch is held to the SET position, voltage will be
present on the PTO Engage Signal circuit at the PCM. The PTO indicator light is integral with the switch and will illuminate when the switch is turned
ON. The presence of the indicator being on does not mean that the PTO Solenoid is engaged. The Cruise Control Multi-Function Switch may be used in
conjunction with the PTO Switch. Illumination of the switch is provided through the dimming circuit and controlled in pan by internal switch logic.
TAC Module
The TAC module is the control center for the electronic throttle system. The TAC module and the PCM communicate through a dedicated redundant
serial data circuit. The TAC module and the PCM monitor the commanded throttle position and compare the commanded position to the actual throttle
position. This is accomplished by monitoring the APP and the Throttle Position (TP) sensor. These 2 values must be within a calibrated value of each
other or a DTC may be set. The TAC module also monitors each individual circuit of the TP sensor and the APP to verify proper operation. The TAC
module commands the TAC motor to increase or decrease the engine RPM.
TAC Motor
The TAC motor is part of the throttle body and controls the positions of the throttle. The motor is bi-directional and is controlled by the TAC module.
