STS RWD V8-4.6L (2007)
Electronic Throttle Actuator: Description and Operation
Throttle Actuator Control (TAC) System Description
TAC System
The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for a mechanical cable.
The TAC system performs the following functions:
* Accelerator pedal position 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 accelerator pedal position (APP) sensors
* The throttle body assembly
* The engine control module (ECM)
Accelerator Pedal Position (APP) Sensor
The accelerator pedal contains 2 individual sensors within the assembly. The accelerator pedal position (APP) sensors 1 and 2 are potentiometer type
sensors, each with the following 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 engine controls module (ECM) provides each APP sensor with a 5-volt reference circuit and
a low reference circuit. The APP sensors provide the ECM with signal voltage proportional to the pedal movement. The APP sensor 1 signal voltage at
rest position is near low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is near low reference and
increases as the pedal is actuated.
Throttle Body Assembly
The throttle body assembly contains the following components:
* The throttle blade
* The throttle actuator motor
* The throttle position (TP) sensor 1 and 2
The throttle body functions are similar to a conventional throttle body with the following exceptions:
* An electric motor opens and closes the throttle valve.
* 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.
TP sensors are sensors 1 and 2 are potentiometer type sensors, they are used to determine the throttle plate angle. The TP sensors provide the engine
control module (ECM) with a signal voltage proportional to throttle plate movement. The TP sensor 1 signal voltage at closed throttle is near the 5-volt
reference voltage and decreases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is near the low reference voltage and
increases as the throttle plate is opened. Each TP sensor has a signal circuit and they both share a 5-volt reference and a low reference circuits.
Engine Control Module
The engine control module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the drivers intent, then
calculates the appropriate throttle response. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the TAC motor.
Modes of Operation
Normal Mode
During the operation of the TAC system, several modes or functions are considered normal. The following modes may be entered during normal
