Forenza L4-2.0L (2004)
Idle Speed/Throttle Actuator - Electronic: Description and Operation
Throttle Actuator Control (TAC) System Description
The Throttle Actuator Control (TAC) system is used to improve emissions, fuel economy and driveability. The TAC system eliminates the mechanical
link between the accelerator pedal and the throttle plate. The TAC system eliminates the need for a cruise control module and idle air control motor. The
following is a list of TAC system components:
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The accelerator pedal assembly includes the following components:
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The accelerator pedal
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The Accelerator Pedal Position (APP) sensor
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The AAP sensor 2
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The throttle body assembly includes the following components:
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The Throttle Position (TP) sensor 1
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The TP sensor 2
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The throttle actuator motor
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The throttle plate
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The Engine Control Module (ECM)
The ECM monitors the driver demand for acceleration with 2 APP sensors. The APP sensor 1 signal voltage range is from about 0.7 - 4.5 V as the
accelerator pedal is moved from the rest pedal position to the full pedal travel position. The APP sensor 2 range is from about 0.3 - 2.2 V as the
accelerator pedal is moved from the rest pedal position to the full pedal travel position. The ECM processes this information along with other sensor
inputs to command the throttle plate to a certain position.
The throttle plate is controlled with a direct current motor called a throttle actuator control motor. The ECM can move this motor in the forward or
reverse direction by controlling battery voltage and/or ground to 2 internal drivers. The throttle plate is held at a 5.7 degrees TPS rest position using a
constant force return spring. This spring holds the throttle plate to the rest position when there is no current flowing to the actuator motor. The ECM
monitors the throttle plate angle with 2 TP sensors. The TP sensor 1 signal voltage range is from about 0.7 - 4.3 V as the throttle plate is moved from 0%
to Wide Open Throttle (WOT). The TP sensor 2 voltage range is from about 4.3 - 0.7 V as the throttle plate is moved from 0% to WOT.
The ECM performs diagnostics that monitor the voltage levels of both APP sensors, both TP sensors and the throttle actuator control motor circuit. It
also monitors the spring return rate of both return springs that the housed are internal to the throttle body assembly. These diagnostics are performed at
different times based on whether the engine is running or not running. Every ignition cycle, the ECM performs a quick throttle return spring test to make
sure the throttle plate can return to the 7% rest position from the 0% position. This is to ensure that the throttle plate can be brought to the rest position in
case of an actuator motor circuit failure.
