K 1500 Suburban 4WD V8-4.8L VIN V (2003)
Electronic Throttle Actuator: Description and Operation
THROTTLE ACTUATOR CONTROL (TAC) SYSTEM DESCRIPTION
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:
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Accelerator pedal position sensing
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Throttle positioning to meet driver and engine demands
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Throttle position sensing
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Internal diagnostics
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Cruise control functions
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Manage TAC electrical power consumption
The TAC system components include the following:
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The accelerator pedal position (APP) sensors
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The throttle body assembly
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The throttle actuator control module
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The powertrain control module (PCM)
Accelerator Pedal Position (APP) Sensor
The accelerator pedal assembly contains 2 individual APP sensors within the assembly. The accelerator pedal position (APP) sensors 1 and 2
potentiometer type sensors each with 3 circuits:
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A 5-volt reference circuit
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A low reference circuit
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A signal circuit
The APP sensors are used to determine the pedal angle. The control module provides each APP sensor a 5-volt reference circuit and a low reference
circuit. The APP sensors then provide the control module with signal voltage proportional to pedal movement. Both APP sensor signal voltages are low
at rest position and increase as the pedal is applied.
Throttle Body Assembly
The throttle body assembly consists of the throttle body, the throttle position (TP) sensors, and the throttle actuator motor. The throttle body functions
similar to a similar to a conventional throttle body with the following exceptions:
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An electric motor opens and closes the throttle valve.
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The throttle blade is spring loaded in both directions and the default position is slightly open.
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There are 2 individual TP sensors within the throttle body assembly.
The TP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
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A 5-volt reference circuit
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A low reference circuit
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A signal circuit
The TP sensors are used to determine the throttle plate angle. The control module provides each TP sensor a 5-volt reference circuit and a low reference
circuit. The TP sensors then 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.
Throttle Actuator Control Module
The TAC module is the control center for the throttle actuator control system. The TAC system is self-diagnosing and provides diagnostic information to
the PCM through a dedicated serial data line. The TAC achieves throttle positioning by providing a pulse width modulated voltage to the TAC as
directed by the PCM.
Powertrain Control Module
The PCM determines the driver's intent and then calculates the appropriate throttle response. This information is sent to the TAC module through a
dedicated serial data line.
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
operation:
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Minimum pedal value-At key-up the PCM updates the learned minimum pedal value.
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Minimum TP values-At key-up the PCM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is
