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 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) 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.
Operating Mode
Normal Mode
In the TAC System Operations, multiple modes or function are considered normal. During normal operation, may enter the following mode:
| • | Minimum pedal value - with ignition key On, the ECM updates the learned minimum pedal value. |
| • | Minimum the throttle position value - with ignition key ON, the ECM updates the learned throttle value. In order to learn the minimum throttle value, the throttle 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 with the engine OFF, 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
If an error is detected in the TAC system, the engine control module (ECM) will go into one reduce engine power modes. Reduces engine power will cause the following one or more conditions occurred:
| • | Limited acceleration - The ECM will continue to use the accelerator pedal for throttle angle control, however, the vehicle acceleration is limited. |
| • | Limited throttle mode - The ECM will continue to use the accelerator pedal for throttle angle control however, the maximum throttle angle is limited. |
| • | Throttle default mode - The ECM will turn OFF the throttle actuator motor and the throttle will return to the spring loaded default position. |
| • | Forced idle mode - The ECM will perform the following actions: |
| - | Limit engine speed to idle status, by positioning the throttle position or the throttle is turned OFF by controlling the fuel and spark plug. |
| - | Ignore the accelerator pedal input signal. |
| • | Engine shutdown mode - The ECM will disable the fuel and de-energize the throttle actuator. |
