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:
| • | Throttle positioning to meet driver and engine demands |
| • | Throttle position sensing |
| • | Manage TAC electrical power consumption |
The TAC system includes the following components:
| • | The pedal position sensors |
| • | The throttle body assembly |
| • | The engine control module (ECM) |
Pedal Position Sensor
The pedal position sensor contains 2 individual sensors within the assembly. The Pedal Position sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
| • | A 5-volt reference circuit |
| • | A low reference circuit |
The pedal position sensors are used to determine the throttle angle. The engine control module (ECM) provides each pedal position sensor a 5-volt reference circuit and a low reference circuit. The pedal position sensors provide the ECM with signal voltage
proportional to the throttle movement. The pedal position sensor 1 signal voltage at rest position is less than 1 volt and increases to above 4 volts as the pedal is actuated. The APP sensor 2 signal voltage at rest position is greater
than 4 volts and decreases to less than 1 volt as the throttle is actuated.
Throttle Body Assembly
The throttle assembly contains the following components:
| • | The throttle actuator motor |
| • | The 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 engine control module (ECM) with a signal voltage proportional to throttle plate movement. The TP sensor 1 signal voltage at closed throttle is approximately
1.5 volts and increases to greater than 4 volts as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is approximately 3.5 volts and decreases to less than 1 volt as the throttle plate is opened.
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 and 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 throttle actuator control (TAC) system, several modes or functions are considered normal. The following modes may be entered during normal operation:
| • | Minimum pedal value--At key-up the engine control module (ECM) updates the learned minimum pedal value. |
| • | Minimum throttle position (TP) values--At key-up the ECM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position. |
| • | Ice break mode--If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in
the closing direction. |
| • | Battery saver mode--After a predetermined time without engine RPM, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used
to maintain the idle position and allows the throttle to return to the spring loaded default position. |
Reduced Engine Power Mode
When the ECM detects a condition with the TAC system, the ECM may enter a Forced idle mode. During the Forced idle mode the ECM will perform the following actions:
| • | Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned off. |
| • | Ignore the accelerator pedal input. |
