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Urea injection systems

The advent of the autonomous car has highlighted the fundamental importance of having good sensors. That being said, we have long been committed to providing effective – and reliable – sensors to our customers. So whether you are looking for engine and transmission sensors, or for comfort and safety – not to mention emissions and e-mobility – you should definitely take a look at our range.

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Urea
injection systems

The urea injection system, also known as the SCR (Selective Catalytic Reduction) system, is used in diesel vehicles to reduce NOx (nitrogen oxide) emissions.

Urea, a chemical compound, is stored in a separate tank in the form of a solution called AdBlue® (which is made up of approximately 32.5% urea and 67.5% demineralized water). This solution is injected into the exhaust system, upstream of the SCR catalytic converter, where it is converted into ammonia (NH₃) due to the heat of the exhaust gases.

The role of the SCR system is to reduce nitrogen oxides (NOx), which are harmful pollutants for the environment and health. When ammonia reacts with the NOx in the SCR catalytic converter, a chemical reaction occurs, converting the NOx into nitrogen (N₂) and water (H₂O), both of which are harmless to the atmosphere.

Environmental standards, such as Euro 6 in Europe, impose strict limits on vehicle pollutant emissions. The urea injection system enables diesel engines to comply with these standards without affecting engine performance too much. It is therefore an effective solution for reducing the environmental footprint of diesel vehicles while maintaining their performance levels.

Technologies
Technical information
Frequently asked questions
Resources
Technologies

The urea injection system consists of the following components in order to operate efficiently:

  • The AdBlue® tank: This is a specific tank that stores the urea solution (AdBlue®). It is designed to keep this solution at a stable temperature, as AdBlue® freezes below -11°C. Heating systems are often integrated to ensure that the solution remains liquid in cold conditions.
  • The injection module: This is a pump that injects a precise quantity of AdBlue® into the exhaust stream, just upstream of the SCR catalytic converter. The vehicle’s ECU regulates this injection according to data collected by various sensors, including data measuring exhaust gas temperature and emissions levels.
  • The SCR catalytic converter: This is where the key chemical reaction takes place. The catalytic converter is generally made up of materials such as titanium, vanadium, or rare metal oxides. When the ammonia (NH₃) resulting from the AdBlue® decomposition comes into contact with the nitrogen oxides (NOx), the nitrogen oxides are converted into harmless nitrogen (N₂) and water (H₂O) vapor.

Technical information

SYMPTOMS

The following symptoms are frequently associated with the failure of an urea injection system:

  • Indicator light on the dashboard;
  • Reduced engine performance;
  • Excessive AdBlue® consumption;
  • Abnormal exhaust smell;
  • Downgrade mode of the engine;
  • Increased emissions;
  • Excessive smoke emissions.

DIAGNOSTIC PROCEDURE

Firstly, it is necessary to check the AdBlue® level and quality. A low level may activate warnings and reduce system performance. The AdBlue® must be pure, as impurities or a diluted solution can damage the injection system and the catalytic converter. If necessary, replace the AdBlue® and clean the tank.

It is also important to visually inspect the various components of the urea injection system, in order to determine whether there is any visual fault.

If this is not sufficient, the use of an OBD-II diagnostic tool is recommended to identify the fault codes associated with the urea injection system. For example, codes such as P20E8 (low AdBlue® level) or P207F (reduced SCR system efficiency) may indicate issues with the urea injection system.

The OBD tool also monitors data from the NOx, temperature, and pressure sensors in real time. This can indicate whether a specific part is operating abnormally. Indeed, if these sensors are faulty, they can affect the operation of the urea injection system.

If the preceding tests are inconclusive, your vehicle’s urea injection system needs to be replaced.

 

CAUSES OF FAILURE

An urea injection system may no longer be working due to:

  • AdBlue® pump or injector failure;
  • NOx sensor failure;
  • An issue with the catalytic converter; or
  • A lack of AdBlue®.

INSTALLATION INSTRUCTIONS

To ensure fast and efficient installation, please refer to the following instructions:

  1. Disconnect the vehicle battery’s negative terminal.
  2. Empty the AdBlue® tank.
  3. Disconnect the connectors connected to the tank, as well as the fluid lines.
  4. Remove the fixings using a ratchet wrench to unscrew the bolts. Depending on the model, the tank may be fitted under the vehicle or in a specific compartment.
  5. Carefully remove the tank.
  6. Locate the injector, which is usually located upstream of the SCR catalytic converter on the exhaust system.
  7. Disconnect and remove the injector.
  8. Install the new injector, following the reverse procedure. Make sure that it is properly secured, and reconnect the electrical cables as well as the AdBlue® lines.
  9. Reposition and reconnect the tank.
  10. If the vehicle is fitted with a heating system to prevent the AdBlue® from freezing, check that all of the connections are in place and that the system is operational.
  11. Reconnect the vehicle’s battery.
  12. Using the OBD-II tool, reinitialize any error codes that may be linked to the SCR or emissions systems.

INSTALLATION TIPS

As the urea injection system is essential to the correct operation of the exhaust system, it is important to follow certain advice in order to prolong its service life:

  • Replace the upstream and downstream NOx sensors (depending on vehicle model) at the same time as the urea injector;
  • Replace the AdBlue® tank at the same time as the urea injector.

PREVENTIVE INFORMATION

The above items are provided for information purposes only. They do not replace the advice of a qualified technician or mechanic. We strongly recommend that you consult a professional if you are unsure of what to do. Otherwise, we cannot accept responsibility for any damage to your vehicle.

Frequently asked questions
What symptoms should I look out for?

Most vehicles fitted with a urea injection system have specific warning indicator lights that will indicate if there is an issue linked to any failure. Sometimes, an engine check indicator light may also come on. It is very likely that engine power will be limited to avoid increasing pollutant emissions. This can result in a drop in performance, reduced acceleration, or irregular engine behavior. If the injection system is not working properly, it may overconsume the AdBlue® solution. Due to poor NOx management, your vehicle may emit more smoke or darker smoke. If the urea is not injected correctly or if the chemical reaction in the catalytic converter does not take place as expected, you may detect an unusual smell coming from the exhaust, which is linked to incorrectly processed gases. In some cases, to protect the engine and limit emissions, your vehicle may switch to downgrade mode. This considerably reduces the maximum speed and overall performance, making driving difficult until the issue is resolved. Malfunctioning of the SCR system leads to increased pollutant emissions, especially nitrogen oxides (NOx). This issue may be detected during a technical inspection or an emissions test, where the vehicle fails to meet pollution standards.

How to identify the fault?

Firstly, we strongly recommend that you check the AdBlue® level and quality. A low level may activate warnings and reduce system performance. The AdBlue® must be pure, as impurities or a diluted solution can damage the injection system and the catalytic converter. If necessary, you should replace the AdBlue® and clean the tank.

We also suggest that you visually inspect the various components of the urea injection system, in order to determine whether there is any visual fault.

If this is not sufficient, the use of an OBD-II diagnostic tool via a professional is recommended to identify the fault codes associated with the urea injection system.  For example, codes such as P20E8 (low AdBlue® level) or P207F (reduced SCR system efficiency) may indicate issues with the urea injection system.

The OBD tool also monitors data from the NOx, temperature, and pressure sensors in real time. This can indicate whether a specific part is operating abnormally. Indeed, if these sensors are faulty, they can affect the operation of the urea injection system.

If the preceding tests are inconclusive, then it would appear that you will need to replace your vehicle’s urea injection system.

Why does my urea injection system need replacing?

Although vehicle sensors meet very strict standards, they do not last forever. A number of factors may result in the need to replace them, including failure of the AdBlue® pump or injector. It is also worth mentioning the failure of NOx sensors: If the sensors are not detecting the NOx levels correctly, the system will not be able to adjust the quantity of urea to be injected. The SCR catalytic converter can also become clogged or deteriorate, reducing its effectiveness in processing NOx. A simple lack of AdBlue® solution can also cause system malfunctions, which is why it is important to check the level first.

What are the installation instructions?

We recommend that you follow the steps below to replace your urea injection system as efficiently as possible and to minimize the risk of any error:

    1. Disconnect the vehicle battery’s negative terminal.
    2. Empty the AdBlue® tank.
    3. Disconnect the connectors connected to the tank, as well as the fluid lines.
    4. Remove the fixings using a ratchet wrench to unscrew the bolts. Depending on the model, the tank may be fitted under the vehicle or in a specific compartment.
    5. Carefully remove the tank.
    6. Locate the injector, which is usually located upstream of the SCR catalytic converter on the exhaust system.
    7. Disconnect and remove the injector.
    8. Install the new injector, following the reverse procedure. Make sure that it is properly secured, and reconnect the electrical cables as well as the AdBlue® lines.
    9. Reposition and reconnect the tank.
    10. If the vehicle is fitted with a heating system to prevent the AdBlue® from freezing, check that all of the connections are in place and that the system is operational.
    11. Reconnect the vehicle’s battery.
    12. Using the OBD-II tool, reinitialize any error codes that may be linked to the SCR or emissions systems.
What tips should I use to extend the life of my urea injection system?

As the urea injection system is essential to the correct operation of the exhaust system, it is important to follow certain advice in order to prolong its service life:

  • Replace the upstream and downstream NOx sensors (depending on vehicle model) at the same time as the urea injector;
  • Replace the AdBlue® tank at the same time as the urea injector.
Resources
This tab contains all the documents available relating to urea injection systems.
Summary sheet
Find out more about urea injection systems.
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