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:
Antilock Brake System (ABS) Warning Light
This light comes on briefly when the engine is started.
If the light stays on, turn the ignition to LOCK/OFF or if the light comes on,
stop as soon as possible and turn the ignition off. Then start the engine again
to reset the system. If the light still stays on, or comes on again while driv ...
Tire Rotation
In order to equalize wear, rotate the tires at the specified intervals. Also,
rotate the tire and wheel assembly whenever you notice uneven tire wear.
Radial tires tend to wear faster in the shoulder area, particularly in front
positions, due to design. Radial tires in non-drive locations may ...
Range Selector Lever Cable Bracket Replacement
Removal Procedure
Set the park brake and chock the wheels.
Disconnect the range selector cable end (1) from the
range selector lever.
Disconnect the range selector cable (2) from the range
selector cable bracket.
Remove the transmission rang ...
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