Chevrolet Sonic Repair Manual: Throttle Actuator Control (TAC) System Description
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The engine control module (ECM) is the control center for the throttle actuator
control (TAC) system. The ECM determines the driver's 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?t key-up, the ECM updates the learned minimum pedal
value.
- Minimum throttle position values?t 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?f 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.
- Minimum pedal value?t key-up, the ECM updates the learned minimum pedal
value.
- Battery saver mode?fter 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
reduced engine power mode. Reduced engine power may cause one or more of the
following conditions:
- Acceleration limiting?he ECM will continue to use the accelerator pedal
for throttle control, however, the vehicle acceleration is limited.
- Limited throttle mode?he ECM will continue to use the accelerator pedal
for throttle control, however, the maximum throttle opening is limited.
- Throttle default mode?he ECM will turn OFF the throttle actuator motor,
and the throttle will return to the spring loaded default position.
- Forced idle mode?he 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?he ECM will disable fuel and de-energize the throttle
actuator.
Install a NEW throttle body seal.
Install the throttle body (1).
Caution: Refer to Fastener Caution.
Install the 4 throttle body bolts (2) and tighten to ...
Other materials:
Front Seat Cushion Cover and Pad Replacement
Front Seat Cushion Cover and Pad Replacement
Callout
Component Name
Warning: Refer to SIR Warning.
Preliminary Procedures
Remove the driver or passenger seat. Refer to Driver or Passenger
Seat Removal and Inst ...
Control Valve Body Cover Replacement
Removal Procedure
Disconnect the battery negative cable. Refer to
Battery Negative Cable Disconnection and Connection.
Raise and support the vehicle. Refer to
Lifting and Jacking the Vehicle.
Remove the front bumper fascia opening lower cover.
Refer to Front Bumper ...
Steering wheel
General information
Make sure that:
The distance between your upper body and the
steering wheel is at least 10 inches (25 cm)
Your arms are bent slightly at the elbows
You have a sufficient view of the area around
the vehicle and you have a clear view of the instrument
cluster and head-up dis ...
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