What does error code P0120 mean and how to fix it?

What is an error code P0120, what causes it and how to fix it

If any problems with the engine occur in the car, it is usually accompanied by the inclusion of the Check or Check Engine light on the dashboard. But not always such a signal indicates that there is a critical malfunction, without eliminating which it is strictly forbidden to operate the car.

Quite often, the electronic control unit, or simply the ECU, generates errors that are not critical. But they still provoke the activation of the warning on the panel about the need to check the engine.

Ignoring any error, including P0120, can potentially lead to serious consequences. Therefore, you should definitely check the engine, determine the nature of the malfunction and try to eliminate it. With your own efforts or with the help of car-care center, the question is not a matter of principle.

Error code P0120 indicates that there are problems with the throttle position sensor assembly or malfunction in its electrical circuit.

What this sensor is used for and how it works

Before eliminating the error in question, it is necessary to understand which sensor we are talking about, what it does and how it functions.

The throttle position sensor is located in the throttle body. It is responsible for fixing the angles of rotation when the damper works.

Structurally, it is a fairly simple device. This allows it to work for many years, without causing problems for the engine and the car owner. There are a number of examples, when this sensor was undisturbed for 200-300 thousand km.

The position sensor has two circuits. One is used for analysis of the throttle position data in a specific time interval. The second circuit monitors the operation of the first.

Depending on the degree of opening or closing of the choke the parameters of feeding voltage coming from the sensor to the ECU change. If the damper is closed, the voltage is 0 V. In some cases it may be up to 0,5 V. If the damper is in fully open position, the value rises to 5 V.

Accordingly, when the opening angle is changed, this voltage is constantly changing within a given range.

The ECU, receiving data from the throttle sensor, can determine when it is necessary to increase or decrease the volume of fuel supplied, decrease or increase revolutions, etc.

If this controller is working properly, the engine works in the optimal mode depending on the specific operating conditions.

This gives an indication of how important the controller in question really is.

Signs of malfunctions

There are several symptoms that usually show up if the error P0120 in the electronic unit of the car pops up.

They are quite expected and obvious, given the functions performed by the sensor.

The engine enters emergency operation mode. The essence of the emergency mode consists in stopping the automatic control of the damper depending on the specific operating conditions and load. If the emergency mode is activated, then the damper stops in a certain position and is fixed by the return spring. This causes the power to drop instantly. In many cars, the electronic unit switches on the speed limiter. As a result, it is not possible to accelerate up to more than 50-60 kilometers per hour even with full throttle.
RPMs are actively floating at idle. There are also cases with certain cars, when after a short work at idle the engine stalls. Revolutions constantly have to be maintained with the gas pedal.
The fuel consumption level increases. The sensor does not send the necessary information to the ECU, and therefore the latter can not form the optimal proportions for the fuel-air mixture. More fuel is supplied to the cylinders, the consumption rises.

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Symptoms when error P0120 occurs may differ depending on the particular car and the ECU settings used. But in most cases, they correspond to the signs described.

Under what conditions the error is formed

In order to see error P0120 on a car, certain conditions must be formed for its occurrence. This is done without any special participation of the motorist himself.

Before an error code P0120 is written into the ECU memory of a Nissan, Mitsubishi or other car brand and the motorist notices the malfunction, certain events should occur:

Parameters of the maximum allowable voltage depend on the specific machine and the ECU software used.
This problem lasts longer than the time interval set in the software. For example, the voltage rises for 2 seconds or more.

There are some cars where the error in question appears after the accelerator pedal has been pressed to the floor.

In most cases an error code P0120 is recorded in the ECU memory after the first trip, when the malfunction was detected and the corresponding conditions were created.

That is, the ECU does not need much time to notify the driver about the problem with the sensor.

Why the error occurs

Now one of the key questions. You need to find out the reason why an error code with the value P0120 may appear in the memory of the electronic unit.

There are only a few reasons for such an error to occur.

There are problems with the position sensor. Basically, the problems are understood to be wiring breakage or short circuit in the sensor circuit. Breakdown of the controller itself is unlikely. But it should be checked just in case.
There are problems on the throttle body side. It is considered to be a more serious fault. It leads to the consequences, the danger of which is much more dangerous than just showing the error and turning on the check engine light on the dashboard. The body is usually deformed when there is a strong mechanical shock. It can be an accident, an accident, a deliberate blow to this area. Damage to the case as a result of oxidative processes and severe contamination cannot be ruled out.
Errors in the software of the electronic unit. Rare malfunction. But it happens. And almost always we are talking about those ECUs, which have been previously re-flashed and the factory settings have been changed. If the ECU is running on native software, the probability of seeing error P0120 because of it is extremely low.

The sensor is part of the throttle valve. Because of this, it is unlikely to fail, plus it is almost impossible to replace it separately.

If it does have to be replaced, then a new throttle with the sensor already in it will have to be installed.

Since there are few potential causes, this makes it much easier to find the problem quickly and try to fix it yourself. If it fails, you can always call a car service.

Troubleshooting

Depending on what causes the error with code P0120 came up, the process of its elimination will be appropriate.

All the methods under consideration are applied on different cars. Everywhere, the error P0120 is eliminated approximately according to an identical algorithm.

It is only important to take into account that the position of the flap itself and the sensor may differ depending on whether you are working with Mitsubishi, Nissan, Mercedes or the same Renault cars.

If the error with code P0120 appeared, you can take the following actions.

Carry out diagnostics of the sensor. The vast majority of modern cars, in which the error P0120 appears, the sensor acts as a component of the throttle itself. That is, in order to perform diagnostics and eliminate the causes, due to which the P0120 error has appeared, you will have to dismantle the entire element. And this involves disassembly of an impressive part of the under-hood space and the motor. Such work is not recommended to carry out on your own. It is difficult. Plus the diagnostics is performed with specialized equipment. If the check shows that the sensor is out of order, which is extremely rare, you will have to remove the entire throttle and replace it as a whole.
Check the choke operability. Usually, P0120 error occurs not because of the sensor, but because of malfunction in the choke itself. Very often it is simply contaminated, there are traces of oxide and rust on its surfaces, the choke is covered with debris. Therefore, the first thing to do is a comprehensive cleaning. To clean the choke, a liquid designed for carburetor cleaning is perfectly suitable. When checking the assembly, make sure that the return spring is in good condition. The presence of traces of mechanical damage indicates the need for replacement.
Check the condition of electrical circuits. Using a diagnostic scanner or an ordinary multimeter, you can check the 2 circuits with which the throttle sensor is connected. Compare the results with the normal parameters specific to your particular car. Usually this is a voltage range of 0 to 5 V.
Carry out ECU diagnostics. Here you will need a diagnostic scanner, which you use to connect to the ECU. If the error is related to software failures, additionally, when checking, other errors should appear besides P0120.

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The error considered is not critical. But it can provoke transition of an internal combustion engine into the emergency mode. And this will not allow normal operation of the car.

The error is necessarily removed, having previously eliminated the cause of its appearance.

How to remove the error

The error can be reset in two ways.

The first involves the use of plug-in devices and software. Some scanners allow you not only to watch, but also to erase errors, or to use computer programs. There are specialized official and unofficial software for different machines.

The second option is quite severe. For it, the minus terminal is removed from the battery for 10-15 seconds, and put back in place. This clears the ECU memory and forcibly erases the errors. If P0120 appeared by mistake, or the cause of the occurrence is eliminated, then after resetting the terminal the ECU will reboot and re-diagnose the systems.

After resetting the error by disconnecting the battery, throttle adaptation must be performed. Otherwise, another error will occur.

Adaptation instructions are usually provided in the manual for each particular car. All have their own sequence.

P0120 – Error code value

Error P0120 is diagnosed as “Throttle/pedal position sensor/switch “A” circuit malfunction. This error is not critical, but it leads to the fact that the car loses dynamics, stops to gain speed normally, jerks, and in some cases “floats” revolutions of the engine. In principle, you may operate the vehicle with such malfunctions, however undesirable. Therefore, at the slightest opportunity, it is necessary to find out the cause of the breakdown and get rid of it.

Throttle position sensor description

Throttle position sensor (in English has the abbreviation TP or TPS) is installed directly on the throttle body. Its main task is to fix the angle of rotation of the throttle. The sensor itself is non-contact and operates on the Hall effect. This ensures its reliability and accuracy of outgoing data.

The sensor is designed with two circuits that transmit information signals, VTA1 and VTA2. The first circuit is used directly to track throttle rotation at a specific point in time, and the second circuit monitors the correct operation of the first. Depending on the turn angle value, a voltage ranging from 0 (some cars 0.45V) to 5 volts DC is sent through the signal wire from the sensor to the electronic control unit (ECU). When the damper is closed, the voltage decreases, and vice versa, if the damper is open, the voltage increases.

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The ECU uses the information coming from the sensor to control the engine (additional fuel supply, speed regulation, etc.). This information is also necessary for adjusting fuel/air ratio to create a fuel mixture with optimal composition, to increase or decrease power.

Vehicle behavior

The first thing the driver sees when error P0120 occurs is a glowing Check Engine warning light on the dashboard. In this case, it is necessary to perform additional diagnostics in order to identify the code of a particular error with the help of special hardware and software (error scanner). A good option for such a task would be Scan Tool Pro Black Edition (an affordable device with wide functionality and compatibility with cars).

Scan Tool Pro Black has a 32-bit PIC18F25k80 chip, which allows you to easily connect to the ECU, not just read the error codes and reset them, and monitor the operation of sensors, save the report, change settings. It can diagnose engine blocks, gearboxes, transmissions, ABS, ESP, etc… It has lossless communication with the ECU via wi-fi or Bluetooth.

With this scanner you can see in real time if the damper actuator is powered and how much it is open.

As for the behavior of the vehicle itself, when an error occurs with code P0120, the electronic engine control unit automatically enters the emergency operation mode. In particular, it cuts off the fuel supply electrically to the throttle motor programmatically. The choke is then set at an angle of 6° by a return spring, and remains in this position until the malfunction is corrected. The ECU controls the engine by reducing the fuel supply (in particular the so-called intermittent cut-off) and the ignition advance angle, which is set according to the angle of the accelerator pedal, in order to keep the vehicle moving at a minimum speed.

That is, if you slightly press and hold the mentioned pedal, the car will move slowly (usually the speed in emergency mode does not exceed 40. 50 km/h). This is the answer to the frequent question of motorists, faced with error P0120, who complain about the fact that the car does not develop revolutions. As it is already clear, this is done intentionally, and is an emergency driving mode. This is how the car will drive until the breakdown is corrected (i.e., the error is fixed) or simply the ignition is turned off (the engine is stopped).

Some car owners say that when the error P0120 occurs, the car jerks and reacts badly to the accelerator pedal. The engine idle speed may also “float”. Naturally, it is uncomfortable to drive a car in such conditions, so it is desirable to diagnose and repair the failure as soon as possible.

Rules of formation of conditions of occurrence

The ECU signals the formation of P0120 error if the output voltage from the VTA1 sensor circuit is for a short time out of the normal range with the accelerator pedal depressed. The program logic is configured in such a way that the error is detected in one trip on the car.

In different car brands (e.g. in Opel or Renault) the value of time and boundary voltages may differ, although insignificantly. As an example, let’s take a popular car Toyota RAV4. Boundary value of output voltage on the sensor is the above mentioned 0 and 5 volts. The time during which the voltage leaves the specified corridor is two seconds.

Many motorists note that error P0120 often appears when the engine is running at high RPM for a long time. For example, when driving on a bad road with a heavy load. That is, when the accelerator pedal is significantly depressed. Although, of course, there are exceptions.

The main causes of occurrence

The throttle position sensor has a fairly simple device, so there are few reasons why it may fail. So, the causes of the error P0120 can be:

A faulty throttle position sensor. Since the sensor is mounted directly on its body, it is not possible to remove it in most cars. Most often there is a wire break or short circuit in the electrical circuits of the sensor.
Throttle body . It can be damaged for a variety of reasons, from commonplace contamination to exposure to a variety of mechanical damage, such as impact or significant pressure. Damage to the throttle body can affect the performance of the throttle sensor.
Electronic engine control unit . In some cases (in fact, quite rarely) the ECU may give a false signal about the occurrence of error P0120. This is due to failures in its electronics (hardware and/or software).

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There are actually four variants of error P0120 . Specifically, the English-language program designates them as follows:

2009 (008) M16/6 (Throttle valve actuator)Actual value potentiometer, N3/10 (ME-SFI [ME] control unit)[P0120] (throttle valve actuator).
2009 (004) M16/6 (Throttle valve actuator)Actual value potentiometer, Adaptation Emergency running [P0120] (adaptation start error).
2009 (002) M16/6 (Throttle valve actuator) Actual value potentiometer, Return spring[P0120] (return spring error).
2009 (001) M16/6 (Throttle valve actuator)Actual value potentiometer, Adaptation[P0120] (adaptation error).

In fact, there aren’t many reasons that can cause error P0120. And their localization is usually not a problem.

Checking methods and solutions

The method of fixing the breakdown should be chosen based on the analysis of the causes that led to it. In particular, you need to check the nodes listed below.

Throttle sensor . As mentioned above, the sensor is part of the throttle, so it cannot be dismantled. Therefore, in most cases, it makes sense to remove the entire unit, to make a revision. However, it is necessary to perform such work only if you have a clear understanding of the algorithm of the procedure. Otherwise, it is better to ask for help at a car service center or a service station. Some car owners also advise to perform a check of the car’s crankcase gas ventilation system. If the sensor is defective, then its repair is hardly possible. In the worst case scenario, you need to buy a new throttle valve assembly and replace it. To reduce money costs, it makes sense to buy a used unit (for example, at an auto bazaar or services engaged in disassembly of old cars).

The exception is the commercially available throttle position sensors designed for mechanically controlled throttles. That is, with the use of a cable from the gas pedal. In this case, you can buy a new sensor and replace it.

Throttle valve assembly . It is noted that often the cause of the error P0120 in the ECU is a dirty throttle valve. It is also possible that some foreign object (debris) got into its working area. In this case, it is necessary to revise the throttle valve and clean it. This procedure is not complicated and even a novice car owner can easily cope with it. For cleaning, it makes sense to use special cleaning compounds, for example, agents for cleaning carburetors.

If cleaning the choke did not help, it is necessary to do additional diagnostics. In particular, check the condition of the damper motor and the condition of the return spring. Unfortunately, flap repair is not always possible, and on many cars this unit is considered unrepairable at all (for example, on some models of Renault). Therefore, to get rid of error P0120, it is often necessary to buy and install a new throttle valve.

When performing repair work, some car owners also advise to dismantle the manifold, clean it, inspect the gaskets (rings, replace if necessary), lubricate them with sealant.

Electronic engine control unit . In rare cases, complex electronics fail due to hardware or software errors. This is particularly true for models where the ECU is located in close proximity to the cylinder block (e.g. for some Opel models). As a consequence, the ECU heats up and can give wrong signals. This applies not only to error P0120, but also to many others.

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Therefore, in case the ECU has “malfunctioned”, it will give out not one, but several errors. When such a breakdown is suspected, self-diagnostics and repair is impossible. The mentioned procedures should be performed at service centers, using special additional equipment.

For reference, here is the data about the voltage value of the output signal in the circuit VTA1 of the throttle position sensor. The data is actual for the car Toyota RAV4, but other cars values will be identical or differ slightly. So:

accelerator pedal fully released – 0.5. 1,1 В;
accelerator pedal fully depressed – 3,3. 4,9 В.

Sensor electrical circuits . The easiest and most effective method of diagnostics is to use the software for reading the ECU faults. There are a lot of such programs, respectively, their interfaces are also different, so it makes no sense to describe their work. With their help it is necessary to know voltage on VTA1 and VTA2 circuits in different situations (including emergency mode and at different engine speeds).

Let’s give an example for the already mentioned Toyota RAV4, the sensor connection diagram of which you can see in the picture. So, the following situations are possible:

Flap position (VTA1), with the accelerator pedal released	Choke position 2 (VTA2) with released gas pedal pedal	Choke position (VTA1) with accelerator pedal depressed.	Choke position No. 2 (VTA2), accelerator pedal depressed	Defective section
0-0,2 В	0-0,2 В	0-0,2 В	0-0,2 В	Open circuit in VC circuit
4,5-5,0 В	4,5-5,0 В	4,5-5,0 В	4,5-5,0 В	Open circuit in circuit E2
0-0.2 V, or 4.5-5.0 V	2.4-3.4 V (in fault mode)	0-0.2 V, or 4.5-5.0 V	2.4-3.4 V (in fault mode)	Open or short to ground on VTA1 circuit
0.7-1.3 V (emergency mode)	0-0.2 V, or 4.5-5.0 V	0.7-1.3 V (emergency mode)	0-0.2 V, or 4.5-5.0 V	Open or short to ground on VTA2 circuit
0,5-1,1 В	2,1-3,1 В	3.3 – 4.9 V (not faulty)	4.6-5.0 V (not faulty)	The TP sensor circuit is operating normally.

Remember that after you eliminate the malfunction directly, it is imperative to clear the error information from the ECU memory. In some cases, the information disappears by itself, but if it did not happen in automatic mode, you need to do it forcibly. Two variants are possible.

The first is to use the software, with the help of which the information about the error was received. The programs have a function of ECU memory clearing. The second variant is more simple and consists in disconnection of the minus terminal for 10. 15 seconds the minus terminal of the battery. Such operation will switch ECU off and after it is switched on again it will reboot and it will have up-to-date information about the state of car’s nodes. Of course, it is preferable to use the first option, but if you do not have a scanner with software, it is quite possible to use the second option.

Diagnosing the malfunction that caused error P0120, if you have an error reader, is not very difficult. As practice shows, to eliminate the malfunction it is often enough to simply make a revision and clean the throttle assembly. And only in rare cases, it is necessary to change the entire throttle together with the throttle position sensor.

Conclusion

Throttle error code P0120 is not critical, and when it occurs, the car is quite usable. However, with it, the electronic engine control unit puts the engine into the emergency mode, in which there is no possibility of dynamic acceleration and full power gain. Therefore it is difficult to drive the car in such conditions.

Therefore, at the slightest opportunity it makes sense to perform an inspection of the throttle valve assembly and, if necessary, perform repair works to eliminate the error. And don’t forget to delete the error from ECU memory afterwards.