Possible causes

– Faulty Electronic Throttle Control System (ETCS) Actuator
– Electronic Throttle Control System (ETCS) Actuator harness is open or shorted
– Electronic Throttle Control System (ETCS) Actuator circuit poor electrical connection

When is the code detected?

The P1129 code is set when the throttle opening angle continues to vary great from target throttle opening angle.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1129 LEXUS Description

Electric Throttle Control System (ETCS) is composed of the throttle motor to operate the throttle valve, the electromagnetic clutch to connect the throttle motor with the throttle valve, the throttle position sensor to detect the opening angle of the throttle valve, the accelerator pedal position sensor to detect the accelerator pedal position, the ECM to control the ETCS and the one valve type throttle body.
The ECM controls the throttle motor to make the throttle valve opening angle properly in response driving condition.
The throttle position sensor which is mounted on the throttle body detects the opening angle of the throttle valve, and it provides feedback to the ECM to control the throttle motor.
If the ETCS has a malfunction, the ECM shuts down the power for the throttle motor and the magnetic clutch, and the throttle valve is fully closed by the return spring.
However, the opening angle of the throttle valve can be controlled by the accelerator pedal through the throttle cable.