Throttle Actuator Control (TAC) System Description (LLD)
Circuit/System Description
The engine control module (ECM) is the control center for the
throttle actuator control (TAC) system. The ECM determines the
drivers intent based on input from the accelerator pedal position
sensors, then calculates the appropriate throttle response based on
the throttle position sensors. The ECM achieves throttle
positioning by providing a pulse width modulated voltage to the
throttle actuator motor. The throttle blade is spring loaded in
both directions, and the default position is slightly open.
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 operations:
| • |
Minimum pedal value-At key-up,
the ECM updates the learned minimum pedal value. |
| • |
Minimum throttle position
values-At key-up, the ECM updates the learned minimum throttle
position value. In order to learn the minimum throttle position
value, the throttle blade is moved to the closed position.
|
| • |
Ice break mode-If the throttle
blade 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 throttle body 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 reduced engine power mode. Reduced engine power may cause
one or more of the following conditions:
| • |
Acceleration limiting-The ECM
will continue to use the accelerator pedal for throttle control,
however, the vehicle acceleration is limited. |
| • |
Limited throttle mode-The ECM
will continue to use the accelerator pedal for throttle control,
however, the maximum throttle opening 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 positioning the throttle position, or by controlling
the fuel and spark if the throttle is turned OFF. |
| |
- |
Ignore the
accelerator pedal input. |
| • |
Engine shutdown mode-The ECM
will disable fuel and de-energize the throttle actuator.
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