Circuit Description
The throttle position sensor is mounted on the throttle body, and has 2 built-in sensors to detect the throttle value opening angle and malfunctions of the throttle position sensor.
The voltage applied to 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. The VTA2 is a signal to indicate the information about the opening value 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 DTC is stored, the ECM shuts down the power for the throttle motor and the electromagnetic clutch, and the throttle valve is fully closed by the return spring.
However, the opening angle of the throttle valve can still be controlled by the accelerator pedal through the throttle cable.
HINT:
After confirming DTC P0120, use the hand-held tester or the OBD II scan tool to confirm the accelerator pedal opening position percentage. Enter the following manus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL.