Functional Description - Throttle Body
The throttle body consists of an Electronic Throttle Control (ETC) motor and redundant Throttle Position Sensors (TPS). To increase engine speed, the throttle blade is opened by a ETC motor inside the Throttle Body allowing increased airflow to the engine. The Powertrain Control Module (PCM) uses inputs from the Accelerator Pedal Position (APP) sensor and various engine sensors, as well as inputs from the Transmission Control Module (TCM) and Braking System Module to determine how much throttle blade opening is necessary.
ETC MOTOR: The ETC motor is controlled using an H-Bridge circuit inside the PCM. An H-Bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. The H-Bridge arrangement is generally used to reverse the polarity/direction of the Direct Current (DC) motor which allows the DC motor to run forward and backwards. The DC motor located in the Throttle Body drives the throttle blade. In order to decrease engine speed, along with spark and fuel delivery changes, the PCM commands the throttle blade closed reducing air flow into the engine and the engine speed decreases. In order to increase engine speed, the PCM commands the throttle blade open, increasing air flow and engine speed. The ETC motor (+) and ETC motor (-) control circuits are Pulse Width Modulation (PWM) to control the amount of throttle blade opening. On a normally functioning throttle body, the duty cycle of the ETC motor should typically not go above approximately 40%. See the figure below for a general configuration and operation of an H-Bridge:
THROTTLE POSITION SENSORS:
The throttle body uses two Throttle Position Sensors (TPS) to monitor the throttle blade position. TPS 1 and TPS 2 are located within the throttle body assembly. Each sensor has its own signal circuit (TPS 1 or TPS 2). Both internal sensors share a common 5-Volt reference circuit (Supply) and a common sensor ground. Each signal circuit provides the Powertrain Control Module (PCM) with a signal voltage proportionate to throttle blade movement. Normally operating sensor signals are opposing to each other as the blade opens and closes in the following manner:
- TPS 1 voltage starts low, approximately 0.5 volts at closed throttle, and increases to approximately 4.5 volts at wide open throttle .
- TPS 2 voltage starts high, approximately 4.3 volts at closed throttle, and decreases to approximately 0.7 volts at wide open throttle .