LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lexus >> 2005 >> SC 430 >> Repair and Diagnosis >> Engine Performance >> System >> SFI System - Diagnostics >> DTC P0121: Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance Problem >> Circuit Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Circuit Description

HINT:

This Electronic Throttle Control System (ETCS) does not use a throttle cable.

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

The voltage applied to the terminals VTA and VTA2 of the ECM changes between 0 V and 5 V in proportion to the opening angle of the throttle valve. The VTA 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 VTA and VTA2, and the ECM controls the throttle motor to make the throttle valve angle properly in response to the driving condition.

If this DTCs is stored, the throttle valve is locked at a certain opening angle.

Fig 1: Throttle/Pedal Position Circuit Description
G02955430Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
DTC DETECTION CONDITION AND TROUBLE AREA

DTC No. DTC Detection Condition Trouble Area
P0121 Difference between VTA1 and VTA2 voltage deviates from malfunction criteria (for 2 seconds)
  • Throttle position sensor
  • bull ECM