How to solve DTC P0122 – Throttle Position Sensor/Switch ‘A’ Circuit Low Input

How to solve DTC P0122 – Throttle Position Sensor/Switch ‘A’ Circuit Low Input – In the article that you read this time with the title How to solve the DTC P0122 – Throttle Position Sensor/Switch ‘A’ Circuit Low Input, we have prepared this article well for you to read and take information in it. hopefully, the contents of the post Article List of DTCs, what we write can make you understand. ok, happy reading.

How to solve DTC P0122 – Throttle Position Sensor/Switch ‘A’ Circuit Low Input

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P0122 is a list of coded troubles indicating that there is a voltage shortage. The ECM / ECU can read this sensor under-voltage, from the voltage sent from the sensor.

And save it as a trouble code on the ECM / ECU. TPS functions to read the angle of the valve open and close the air that will enter the combustion chamber.

How to solve DTC P0122
Drive-by-wire TPS sensor.

this sensor knows how many degrees (angle) is open, adjusts the opening and closing of the throttle position, and reports to the ECM / ECU in the form of DC current. The location of the TPS is usually attached to the BODY THROTTLE

Possible symptoms on the DTC car show code P0122

  • The engine indicator light is on / the check engine is on
  • The gas doesn’t want to be small (the engine is rich in gas continuously) or vice versa
  • The car engine is difficult to start
  • The car is running slowly

Possible causes of DTC showing code P0122

  • Improper throttle position
  • Lack of voltage on the sensor
  • TPS sensor stuck/damaged
  • There is an electric short
  • Poor ECU/ECM (damaged)

How to solve Diagnostic Trouble Code P0122

How to solve problems like this clean the throttle body. a stuck/unable to move throttle causes this sensor to not work properly, make sure there are no open wires if there are open wires leading to the sensor and sticking to the body (machine) resulting in a lack of voltage sensor.

Turn on the contact to the on position if the sensor sounds it indicates the sensor is in correct condition. Erase fault codes with car diagnosis tool/scanner. Sometimes just removing the battery can’t clear the error code. Replace the sensor if the sensor is really weak.

This solution can be easily solved if you are familiar with the function and how the TPS sensor works. So, please continue reading this article to understand the work of the TPS sensor and also its function.

Throttle Position Sensor Function

A throttle Position Sensor or TPS is installed in the throttle body and is always in contact with the throttle valve or gas valve. This TPS sensor functions to detect changes in the position of the gas throttle and then converts it into an electrical signal which will be sent to the ECU as an input signal. In addition to these main functions, the ECU also functions TPS to provide information on several things, namely:

  • Engine mode when the gas throttle position is closed (in the idle/stationary position), half-opened, and when fully opened.
  • Used as emission control when the gas throttle position is fully open and when the AC switch is off.
  • As a correction of the air-fuel mixture ratio.
  • As a correction of increased power in the engine.
  • And. as a control for stopping fuel when the engine is in the deceleration position.

Read more: ECM vs PCM vs ECU what are the differences?

Due to the information obtained by the ECU as mentioned above, it is hoped that engine performance can be maximized later. The characteristics of this TPS sensor are that it is always next to the throttle valve or gas valve. The change in the magnitude of the output voltage signal or the sensor output voltage depends on the position of the throttle valve opening. TPS that is often used in injection vehicles is the variable resistor and point contact model.

1) TPS Variable Resistor model

This variable resistor model TPS uses a resistor as a change in the magnitude of the sensor output voltage signal, this sensor uses three cables, namely the input voltage cable (VC), the output voltage cable (VTA), and the mass cable (E2). The voltage used in this variable resistor model TPS sensor uses a voltage from the ECU of 5 voltages.

Throttle Position Sensor
TPS sensor Variable Resistor Type.

The comparison between the gas throttle opening and the amount of voltage released by this TPS sensor is directly proportional, and the ratio between the gas throttle opening and its resistance or resistance is inversely proportional. When the idle position, the voltage released by the TPS sensor is between 0.6 – 0.9 volts, while when the throttle valve is fully open, the voltage released by the TPS sensor is between 3.5 – 4.7 volts. To clarify, it can be seen in the image below about the TPS electrical diagram of the variable resistor model.

2) TPS Contact Point Model

Throttle Position Sensor
TPS Contact Point Model.

This point contact model TPS sensor serves to detect changes in gas throttle openings and the terminals used on the point-contact type TPS sensor are also the same as the variable resistor type TPS sensor, namely by using three wires including IDL, PSW, and E1 terminals. The detection of this point contact type TPS sensor is only done when the throttle valve is in the 0o – 5o position as the idle position and the cable terminal on the connected TPS sensor is the IDL terminal with terminal E1 as the idle rotation position and when the vehicle is decelerating.

When the throttle valve position is between 6o – 49o, the contact point on the TPS sensor is not connected, so the ECU will detect this position as an intermediate rotation. Meanwhile, when the throttle valve opens from 50o until the throttle valve is fully open, the terminals on the connected TPS sensor are PSW terminals and E1 terminals. In this position, the ECU will detect the position of this TPS as a high rotation or full load. Below is shown an electrical diagram of the point-contact type TPS sensor.

Throttle Position Sensor Works

Now it’s time to talk about how the throttle position sensor works. In the EFI system, a car uses a computer which we often call the car ECU. The car’s ECU in its work receives a lot of input from various sensors.

How to solve DTC P0122
TPS sensor location.

One of the most talked-about engine performance is the throttle position sensor or we often call it the TPS sensor.

But how does the throttle position sensor or TPS sensor actually work? This time I will discuss more the problem of the TPS sensor including how it works.

The throttle position sensor (TPS) is used to monitor the position of the throttle valve in an internal combustion engine. The TPS sensor is usually located on the throttle valve spindle so that it can directly monitor its position.

The TPS sensor is a potentiometer, providing a variable resistance depending on the position of the throttle valve (and hence the name throttle position sensor).

Sensor signals are used by the engine control unit (ECU) as input to its control system. The ignition timing and fuel injection timing (and other potential parameters) are changed depending on the position of the throttle valve, and also depending on the rate of change of that position.

Next, we will discuss how the throttle position sensor works or how the TPS sensor works as follows.

TPS provides onboard controller information about idling, deceleration, acceleration rate, and fully open throttle valve (WOT) condition. TPS is a three-wire potentiometer.

In the first wire, a +5V voltage is applied to the resistive layer of the sensor and the second wire closes the sensor circuit to the ground (car body). The third wire is connected to the potentiometer wiper, thereby changing the resistance and hence the signal voltage is returned to the onboard computer.

Based on the received voltage, the onboard computer can calculate idling (below 0.7V), full load (approximately 4.5V), and throttle valve opening speed.

Full Load Condition? how the throttle position sensor works

At full load, the integrated computer provides further enrichment of the fuel mixture. In deceleration mode (throttle valve closed and engine speed above a certain RPM), the onboard computer shuts down fuel injection. Fuel supply is resumed after the engine speed reaches its idle value or when the throttle valve opens. Some cars allow adjustment of these values.


The TS informs the onboard computer of the idling status. Usually, it has a second contact for the fully open throttle valve (WOT) state.

In most cases, the internal computer provides additional enrichment of the fuel mixture at idle and with the throttle valve fully open.

Each TS contact has two positions – open and closed – where the onboard computer detects three different engine states:

  • Throttle valve closed (idle speed contact closed)
  • Throttle valve opened (idle speed contact and WOT open)
  • And, Throttle valve is fully open (idle speed contact open and WOT contact closed)

Some cars allow a TS set. Under many conditions, the TPS sensor may be damaged or experience problems that interfere with overall engine performance.

You can recognize it through the TPS sensor Faulty sign. By recognizing these signs you can then perform a TPS sensor inspection procedure to further confirm it and then repair or replace your car’s TPS sensor.

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