Throttle Position Sensor: Description and Operation

THROTTLE POSITION (TP) SENSOR




The throttle position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line, the powertrain control module (PCM) calculates the throttle position. As the throttle valve angle changes when the accelerator pedal is moved, the TP sensor signal also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle valve opens, the output increases so that at wide open throttle, the output voltage should be more than 3.3 volts.

Because the position of the throttle valve controls the air supply to the engine, the PCM can modify the fuel delivery based on the throttle angle. For example, power enrichment occurs when the throttle angle approaches wide-open throttle. The PCM looks primarily for changes in the TP sensor output to control fuel delivery. Acceleration enrichment occurs when the throttle angle increases, similar to the accelerator pump on a carburetor equipped vehicle.

Auxiliary Intake Air Control System:

The auxiliary intake air control system supplies additional air to the engine during hard acceleration and when operating under high engine loads. The lower air cleaner (ACL) housing has 2 inlet air ducts. The auxiliary inlet air duct is opened or closed by a vacuum operated door. Manifold vacuum is supplied to the door motor (7) by a vacuum solenoid (4). The solenoid is low side controlled by the powertrain control module (PCM). A constant supply of vacuum pressure is assured by the use of a vacuum check valve (8) and a vacuum storage chamber (6). The auxiliary intake air door is open when there is no vacuum applied. The PCM closes the door for most driving conditions. For diagnosis of the auxiliary intake air system refer to Auxiliary Intake Air System Diagnosis.