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 |
| • | Cruise control functions |
| • | Manage TAC electrical power consumption |
The TAC system components include the following:
| • | The throttle body assembly |
| • | The engine control module (ECM) |
Accelerator Pedal Position (APP) Sensor
The accelerator pedal position (APP) sensor is made up of 2 sensors that
are housed inside one assembly. The engine control module (ECM) supplies a separate
5-volt reference and the low reference circuit for each of the sensors. The 5-volt
reference for APP sensor 1 is supplied from the same source in the ECM as the
5-volt reference for the mass air flow (MAF) sensor and the fuel tank pressure (FTP)
sensor. The 5-volt reference voltage for all of the sensors is supplied on separate
ECM terminals, but the terminals are connected internally to a voltage supply. The
APP sensor 1 sends a signal from the sensor to the ECM indicating the accelerator
pedal position. The ECM actuates the throttle plates based on this information.
Throttle Position Sensors
The throttle position (TP) sensors 1 and 2 are located within the throttle
body assembly. The TP sensors share a common 5-volt reference circuit and a common
low reference circuit. The 5-volt reference circuit is also shared with accelerator
pedal position (APP) sensor 2. The 5-volt reference voltage is supplied on
2 separate engine control module (ECM) terminals, but the terminals are connected
internally to the same voltage supply. Each TP sensor has an individual signal circuit,
which provides the ECM with a signal voltage proportional to throttle the plate movement.
When the throttle plate is in the closed position, the TP sensor 1 signal voltage
is near the low reference and increases as the throttle plate is opened. TP sensor 2
signal voltage at closed throttle is near the 5-volt reference and decreases as the
throttle plate is opened.
Throttle Body Assembly
The throttle body assembly contains the following:
| • | Throttle actuator motor |
| • | Throttle position (TP) sensor 1 and 2 |
The throttle body functions 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. |
The TP sensors are used to determine the throttle plate angle. The TP sensors
provide the control module with signal voltage proportional to throttle plate movement.
Both TP sensor signal voltages are low at closed throttle and increase as the throttle
opens.
Engine Control Module
The engine control module (ECM) determines the driver's intent and then calculates
the appropriate throttle response.
