Throttle Position Sensor: Description and Operation
P0120 Throttle Position SensorNOTE: If DTC P0510 (0203) is displayed with DTC P0120, perform TROUBLE DIAGNOSES FOR DTC P0510 first.
The throttle position sensor responds to the accelerator pedal movement. This sensor is a kind of potentiometer which transforms the throttle position into output voltage, and emits the voltage signal to the ECM. In addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal to the ECM.
Idle position of the throttle valve is determined by the ECM receiving the signal from the throttle position sensor. This one controls engine operation such as fuel cut. The throttle position sensor unit has a built-in "Wide open and closed throttle position switch".
P1120 Secondary Throttle Position Sensor
The secondary throttle position sensor responds to the movement of the throttle motor which is controlled by the TAC module.
This sensor is a kind of potentiometer which transforms the secondary throttle position into output voltage, and emits the voltage signal to the TAC module. In addition, the sensor detects the opening and closing speed and position of the secondary throttle valve and feeds the voltage signal to the TAC module.
Another case is when the secondary throttle valve opening becomes smaller than the ordinary throttle valve opening due to TCS operation. In this case, the signal from the secondary throttle valve is used for engine control. This replaces the signal from the ordinary throttle position sensor. The signal of the secondary throttle valve first enters the TAC module, from where it is sent to the ECM.
P1125 Tandem Throttle Position Sensor
This diagnosis is for tandem throttles (main throttle and secondary throttle). The quantity of intake air is determined by these two throttle valves. A rationality check is then carried out by ECM after monitoring the signals of these two throttle position sensors.