Lucerne V6-3.8L (2007)
Electronic Throttle Actuator: Description and Operation
Throttle Actuator Control (TAC) System Description
Purpose
The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The
TAC system performs the following functions:
* Accelerator pedal position (APP) sensing
* Throttle positioning to meet driver and engine demands
* Throttle position sensing
* Internal diagnostics
* Cruise control functions
* Manage TAC electrical power consumption
The TAC system includes the following components:
* The APP sensors
* The throttle body assembly
* The powertrain control module (PCM)
Accelerator Pedal Position (APP) Sensor
The accelerator pedal contains 2 individual accelerator pedal position (APP) sensors within the assembly. The APP sensors 1 and 2 are potentiometer
type sensors each with 3 circuits:
* A 5-volt reference circuit
* A low reference circuit
* A signal circuit
The APP sensors are used to determine the pedal angle. The powertrain control module (PCM) provides each APP sensor with a 5-volt reference circuit
and a low reference circuit. The APP sensors provide the PCM with signal voltage proportional to the pedal movement. Both APP sensor signal voltages
are low at rest position and increase as the pedal is applied.
Throttle Body Assembly
The throttle assembly contains the following components:
* The throttle blade
* The throttle actuator motor
* The throttle position (TP) sensor 1 and 2
* The throttle actuator control (TAC) module
The throttle body functions similar to a conventional throttle body with the following exceptions:
* There is no longer an idle air control (IAC) motor and associated air passages.
* An electric motor opens and closes the throttle valve.
* The TAC module is located within the throttle body assembly.
* The throttle blade is spring loaded in both directions and the default position is slightly open.
* There are 2 individual TP sensors within the throttle body assembly.
The TP sensors are used to determine the throttle plate angle. The TP sensors provide the powertrain control module (PCM) with a signal voltage
proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens.
Throttle Actuator Control Module
The throttle actuator control (TAC) module is the control center for the TAC system. The TAC system uses electronically erasable programmable read
only memory (EEPROM) and is self-diagnosing. The TAC module provides diagnostic information to the powertrain control module (PCM) through a
dedicated serial data line. The TAC achieves throttle positioning by providing a pulse width modulated (PWM) voltage to the TAC motor as directed by
the PCM. The TAC module is not serviced and should be replaced with the throttle body assembly.
Powertrain Control Module
The powertrain control module (PCM) determines the drivers intent and then calculates the appropriate throttle response. This information is sent to the
