Rendezvous AWD V6-3.6L VIN 7 (2004)
Electronic Throttle Actuator: 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 1
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The APP 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's demand for acceleration with 2 APP sensors. The APP sensor 1 signal voltage range is from about 0.98-4.16 volts 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 0.49-2.08 volts 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 7 percent 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 0.50-4.25 volts as the throttle plate is
moved from 0 percent to wide open throttle (WOT). The TP sensor 2 voltage range is from about 4.45-0.70 volts as the throttle plate is moved from 0
percent 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 are housed internal to the throttle body assembly. These diagnostics are performed at
different times based on whether the engine is running, not running, or whether the ECM is currently in a throttle body relearn procedure.
Every ignition cycle, the ECM performs a quick throttle return spring test to make sure the throttle plate can return to the 7 percent rest position from the
0 percent position. This is to ensure that the throttle plate can be brought to the rest position in case of an actuator motor circuit failure. Observe, under
cold conditions, the ECM commands the throttle plate to 7 percent with the ignition ON and the engine OFF to release any ice that may have formed on
the throttle plate.
Throttle Body Relearn Procedure
The ECM stores values that include the lowest possible TP sensor positions -0 percent, the rest positions -7 percent, and the return rate of both
springs. These values will only be erased or overwritten if the ECM is reprogrammed or if a throttle body relearn procedure is performed. Observe, if
the battery is disconnected, the ECM will immediately perform a throttle body relearn procedure when the ignition is turned ON.
A throttle body relearn procedure is performed anytime the ignition is turned ON, with the engine OFF for longer than 29 seconds when the following
conditions have been met:
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The engine speed is less than 40 RPM.
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The vehicle speed is 0 km/h (0 mph).
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The engine coolant temperature (ECT) is between 5-60°C (41-140°F).
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The intake air temperature (IAT) is more than 5-60°C (41-140°F).
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The APP sensor angle is less than 14.9 percent.
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The ignition 1 voltage is more than 10 volts.
After 29 seconds, the ECM commands the throttle plate from the rest position to full closed, then to around 10 percent open. This procedure takes
about 6-8 seconds. If any faults occur in the TAC system, a DTC sets. At the start of this procedure, the Scan tool TAC Learn Counter parameter
should display 0, then count up to 11 after the procedure is completed. If the counter did not start at 0, or if the counter did not end at 11, a fault has
occurred and a DTC should set.
TAC System Default Actions/Reduce Power Modes
There are 2 reduce power modes that the ECM can default to if an error is detected in the TAC system. If an APP sensor 1 or APP sensor 2 circuit
fault, TP sensor 2 circuit fault or if a TP sensor 1 circuit fault is detected with some APP angle, the ECM goes into one of the 2 reduce power modes.
In this mode, the engine torque is limited so that the vehicle cannot reach speeds of more than 100 km/h (60 mph). The ECM remains in this reduce
power mode during the entire ignition cycle even if the fault is corrected.
If there is a condition with the throttle actuator control circuits, throttle actuator command vs actual position fault, return spring check fault, or a TP
