Circuit Description

The throttle position sensor is mounted on the throttle body. It has 2 sensors to detect the throttle opening angle and a malfunction of the throttle position sensor.

The voltage applied to the terminals VTA1 and VTA2 of the ECM changes between 0 V to 5 V in proportion to the opening angle of the throttle valve. The VTA1 is a signal to indicate the actual throttle valve opening angle which is used for the engine control, and the VTA2 is a signal to indicate the information about the opening angle which is used for detecting a malfunction.

The ECM judges the current opening angle of the throttle valve from these signals input from terminals VTA1 and VTA2, and the ECM controls the throttle motor to make the throttle valve angle properly in response to the driving condition.

When a malfunction is detected, the throttle valve is locked at a certain opening angle. Also, the whole electronically controlled throttle operation is cancelled until the system returns to normal and the ignition switch is turned OFF.

Fig 1: Throttle Pedal Position Sensor/Switch Circuit Diagram

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC P0120, P0122 & P0123 Detection Condition Table

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NOTE:

Fig 3: Main Trouble Area Table

NOTE: When a malfunction is detected, the throttle valve is locked at a certain opening angle. Also, the whole electronically controlled throttle operation is cancelled until the system returns to normal and the ignition switch is turned OFF.

NOTE:

After confirming DTCs, use the hand held tester or the OBD II scan tool to confirm the throttle valve opening percentage and closed throttle position switch condition.
The THROTTLE POS means the VTA1 signal and the THROTTLE POS #2 means the VTA2 signal.
Reference (Normal condition):

Fig 4: Tester Display Table