Service Engine Emissions System 25 Derate: Causes & Fixes

When the warning message “Service Engine Emission System 25 Derate” comes up on your vehicle, it shows something is wrong with the emissions system. This warning does not come alone as it can limit the engine’s power output, making driving quite difficult. 

Many factors could cause the “Service Engine Emission System 25 Derate” to come up. These factors include issues with the DEF doser valve, pump assembly, control module, NOx sensor and a malfunctioning ECM.  

We will look into what the warning message “Service Engine Emission System 25 Derate” means, what could be the causes and how to fix them. 

What is Service Engine Emissions System 25 Derate?

The “Service Engine Emission System 25 Derate” is a warning message that shows something is wrong with the emission system, affecting the engine’s output. Issues with the emission system sensors normally cause this. 

Let’s take this instance: you are driving on the high and having a good time. All of a sudden, your vehicle loses power. You start the engine, and the engine responds; then, you realize that you cannot move past a certain speed. 

Now, you are worried, and suddenly, the warning message “Service Engine Emission System 25 Derate” pops up, accompanied by the engine light and DPF flashing light. 

What, then, is an engine derate? This is when the program in the engine computer system limits power or the speed of the vehicle due to various reasons. However, when it is 25% derate, it is most likely caused by issues with the emission system. 

The emission system is made up of different components; these parts include the following. 

  • DEF Doser Valve 
  • NOx sensors 
  • DEF pump assembly 
  • DEF control module 
  • Engine Control Module (ECM)

If any of these components should fail, it will affect the emission of the vehicle. Once it goes against the program in the ECM, the computer system may trigger the engine system to derate it. 

What is the cause of Service Engine Emissions System 25 Derate?

The warning message “Service Engine Emission System 25 Derate” will be triggered by failing specific emission system parts. Some factors that will cause the warning message include the following. 

1. Damaged DEF doser valve 

The DEF injector is also called the Diesel Exhaust Fluid (DEF) doser valve. It is a device that injects fluid into the exhaust stream of a diesel vehicle. 

In addition, DEF is a mixture of deionized water and synthetic urea. Once the injector releases the fluid into the stream, it immediately breaks down the harmful substances in the emission and can reduce the harmfulness of the gas by up to 90%. 

When the valve or injector is damaged, the fluid cannot enter the exhaust stream. This will affect the vehicle’s emission, releasing harmful environmental gasses. The engine computer system will be able to detect this and, as it goes against its programs, will activate the  “Service Engine Emission System 25 Derate” warning message. 

2. Faulty DEF pump assembly

The function of the DEF pump is to regulate the fluid supply into the exhaust stream properly. It releases the liquid into the emission system through the DEF injector. 

When the pump is damaged or fails, there will be no way the vehicle’s computer system can control the amount of fluid that goes into the system. In most cases, the pump will not supply any of the liquid once damaged, causing increased emissions. 

3. Malfunctioning DEF control module 

The DEF control module controls the operation of the emission system. It is in constant communication with the ECM to ensure the emission process is properly adhered to. 

Once the DEF control module is damaged and fails, the emission system will fail. This means the exhaust gasses will not be purified, and harmful gasses will increase, triggering the warning message. 

4. Damaged NOx sensor 

The NOx sensor is a device that monitors nitrogen oxides in the exhaust system. They serve an important part of the emission system as they constantly feed the engine computer system with information about the vehicle’s emissions.

When the sensor is damaged, the ECM gets the wrong information about the nitrogen oxides in the exhaust gasses or no data. This could lead to the warning message “Service Engine Emission System 25 Derate.”

5. Malfunctioning ECM 

A malfunctioning ECM is another cause of the “Service Engine Emission System 25 Derate” warning message. The computer system controls the vehicle’s emissions, and any fault in the system will affect the quality of gas the vehicle releases. In addition, the ECM can also falsely trigger the warning message. 

How to fix Service Engine Emissions System 25 Derate

Since there are so many causes of the warning message “Service Engine Emission System 25 Derate,” you may need a proper diagnosis. By doing this, you can easily pinpoint the source of the issue. 

There are many ways you can diagnose the problem “Service Engine Emission System 25 Derate.” The most trusted is by using an OBD-II scan tool. Use the tool to get your vehicle’s error codes and solve whichever is related to the warning message. It will be advisable to solve all trouble codes also. 

Below are ways to fix a “Service Engine Emission System 25 Derate” warning message. 

1. Fix damaged DEF doser valve 

In most cases, when your vehicle is faced with a damaged DEF doser valve, it is due to clogged or accumulated dirt. Now, you need to unclog the system. 

All you need to have the valve cleaned or unclogged is basic hand tools and a brass brush. You can use your vehicle’s manual to locate the valve and then have it thoroughly cleaned.

2. Fix faulty DEF pump assembly 

Troubleshooting a faulty DEF pump could be very complicated. Most of the time, people do not diagnose thoroughly before replacing the component. This is why you may need professional help when it comes to pump. 

3. Reset or replace malfunctioning DEF module

If the module of the DEF is malfunctioning, it could be due to several reasons, including the following. 

  • Corroded module 
  • Accumulated dust 
  • Extreme temperature 
  • Low battery voltage 

Below are ways you can fix a DEF issue. 

  • Charge or change vehicle battery. 
  • Drain the vehicle of DEF fluid
  • Replace NOx sensors. 
  • Replace the wire connection of the module. 
  • Clean the doser injectors

4. Replace faulty NOx sensor

The NOx sensor can be found in the exhaust system. There are more than one, and can be seen before and after the selective catalytic reduction (SCR).

Once you can locate the sensors, take them out and examine them for damages like brody body, corrosion, damaged connector, damaged wiring, and more. If the sensor is damaged, the next step is to replace it. 

5. Fix the ECM issue 

Issues with the ECM could be due to software issues or module damage. It is best that a professional troubleshoots issues with the vehicle’s computer system. 

Final Thought!

The “Service Engine Emission System 25 Derate” warning message is best diagnosed and fixed with the help of a professional mechanic. Due to the complicated components of the emission system, it could be hard to have a proper diagnosis and fix done yourself. Find a certified mechanic around you and have your vehicle back in great condition. 

  • Edmond Davis

    I'm Edmond Davis, an automotive expert with years of experience in vehicle repair, performance, and safety. I graduated from the University of Michigan with a degree in Automotive Engineering and have worked with major companies like Ford, GM, and Chrysler. I'm a trusted source of information for anyone looking to learn more about cars or improve their driving experience.

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