Common Diesel Exhaust Fluid Problems | Ultimate Guide

March 12, 2024
def problems

DEF is a key component in the automotive industry's efforts to make diesel-powered vehicles more environmentally friendly.

Many countries and regions have implemented rigorous emission regulations to address air quality concerns. DEF enables diesel engines to comply with these standards, ensuring that vehicles meet the required emission limits and adhere to environmental laws.

DEF usage has become widespread across various industries, including commercial transportation, construction, and agriculture. As a result, DEF has become a standard feature in modern diesel engines.

In this article, we will highlight diesel exhaust fluid problems one may face when handling the fluid for their vehicles, and provide solutions to ensure optimal performance and the longevity of your vehicles.

Understanding Diesel Exhaust Fluid (DEF)

Diesel Exhaust Fluid (DEF) is a solution composed mainly of urea and deionized water. The typical concentration is 32.5% urea and 67.5% deionized water. DEF is a critical component in the Selective Catalytic Reduction (SCR) systems of modern diesel engines.

The primary purpose of DEF is to reduce harmful nitrogen oxide (NOx) emissions produced during the combustion process in diesel engines. 

When injected into the exhaust stream, DEF undergoes a chemical reaction in the SCR catalyst, breaking down NOx into harmless nitrogen and water vapor. 

For additional information on DEF and its composition, visit Fuel Logic's DEF Diesel FAQs.

Common DEF Problems and Their Solutions

def system problems

DEF Contamination

Sharing equipment like funnels or containers previously used for other fluids can introduce foreign substances into DEF. Water contamination can occur if DEF is exposed to moisture during storage, leading to def system problems.

Using as funnels and containers exclusively for DEF can avoid cross-contamination.

Store DEF in clean, sealed containers, and ensure that storage facilities are free from dust and contaminants. Protect DEF from exposure to direct sunlight, as ultraviolet (UV) light can degrade its quality. 

Incase of contamination, you can perform fuel polishing to restore the fluid back to its premium quality.

Incorrect DEF Levels

The SCR system relies on a precise mixture of DEF to catalyze the conversion of NOx into harmless gasses. Incorrect DEF levels can compromise this process, leading to reduced fuel efficiency.

Some vehicles have engine control systems that can initiate derating or limiting engine performance if DEF levels are critically low. Derating helps prevent excessive emissions but can impact overall vehicle performance.

 If DEF levels are too low, the most straightforward solution is to refill the DEF tank. 

If the issue persists, seek professional inspection and assistance. 

DEF Freezing Issues

DEF is a water-based solution containing urea, and when exposed to cold conditions, it may freeze. This can form crystals in the fluid, potentially causing blockages or damage to the DEF system components, such as filters or injectors.

Whenever possible, store vehicles and DEF containers indoors to protect them from extreme cold temperatures. 

Starting the vehicle and allowing the engine to warm up can help thaw the DEF system. Using DEF additives specifically designed to lower the freezing point can prevent DEF from freezing and avoid diesel gelling.

Pump and Injector Problems

Over time, DEF pumps and injectors can experience clogging due to crystallization or contamination in the Diesel Exhaust Fluid (DEF). This can lead to reduced flow, affecting the proper distribution of the fluid, leading to DEF problems.

If there are signs of reduced DEF flow, inspect the pumps and injectors for clogs. Clean or replace components that are obstructed to ensure unimpeded fluid flow.

System Tampering

Modifying the DEF system without proper knowledge and expertise can lead to incorrect dosing of DEF into the exhaust stream. 

To prevent this from happening, follow the vehicle manufacturer's guidelines and recommendations regarding the DEF system. Conduct regular inspections of the DEF system to ensure all components are functioning correctly. 

Additional DEF Challenges and Insights

Troubleshooting diesel exhaust fluid problems is essential to ensure the integrity of the system. Here are some def system problems you may deal with:

Mistakenly Filling Diesel Tank with DEF

Diesel is usually green or black, while DEF is clear or light blue. Pay attention to color coding and labels on fuel pumps and containers to avoid DEF issues.

If you realize that DEF has been added to the diesel tank, do not start the engine. Running the engine with DEF in the diesel system can cause significant damage.

Seek immediate assistance from a qualified mechanic or towing service. Once professional assistance is on-site, the diesel tank needs to be drained thoroughly to remove the DEF. After draining the tank, the mechanic should inspect the fuel system components for any potential damage. 

After confirming that the system is free from DEF, refill the diesel tank with clean diesel fuel. 

Quality Assurance of DEF

The use of high-quality DEF avoids DEF problems, ensuring the longevity of the system and reducing the likelihood of expensive repairs.

Source DEF from certified suppliers. Look for DEF products that carry the API certification mark. This indicates that the DEF meets the ISO 22241 standard, assuring its quality and compliance with industry guidelines.

Consider periodic testing of DEF quality using test strips or kits. Check batch information, including the manufacturing date, ensuring that you are using fresh DEF, and verifying that it has not exceeded its shelf life.

Storage and Handling Best Practices

  • Store DEF in dedicated tanks or containers that are specifically designed for DEF use.
  • Protect DEF from extreme temperatures, as both high heat and freezing conditions can affect its quality.
  • Replace damaged or compromised containers promptly to prevent impurities from entering the DEF.
  • Take measures to prevent water from entering into DEF storage. 
  • Clearly label DEF storage tanks and containers to avoid confusion.
  • Avoid using equipment that has been in contact with other fluids to prevent contamination.
  • Provide training for personnel involved in the handling and storage of DEF to ensure proper procedures are followed.

Impact of DEF on Engine Warranty

Modifying the DEF system without manufacturer approval can void warranties. This includes altering the system's components, tampering with sensors, or using non-approved additives.

Contaminated DEF can damage the SCR system components, leading to potential warranty voidance.

Neglecting recommended maintenance procedures related to the DEF system, such as regular inspections, sensor calibrations, or timely replacement of filters, may impact warranty coverage. 

Always refer to the specific terms and conditions outlined in the manufacturer's warranty documentation for accurate information on warranty coverage and potential voidance factors.

Impact of DEF Quality on Engine Performance

Effect of Poor Quality DEF

Low quality DEF may lack the precise concentration of urea or contain impurities that interfere with the catalytic conversion process.

Incorrect DEF composition can cause chemical reactions leading to def system problems. It can trigger malfunctions in the SCR system, leading to warnings and fault codes.

Engine damage and repair costs

Impurities or chemical additives in poor-quality DEF may contribute to corrosion within the SCR system components, which can lead to the degradation of components such as injectors, sensors, and the SCR catalyst, resulting in def system problems. 

Replacing damaged components and labor costs associated with diagnosing issues and performing repairs contribute significantly to the overall cost of addressing DEF-related damage.

The time required for repairs and the vehicle or machinery's downtime can impact productivity and operational efficiency. 

If engine performance is compromised due to poor-quality DEF, there may be additional costs associated with addressing derating issues and restoring optimal engine functionality.

Advanced DEF Management Techniques

Utilizing technology for monitoring DEF quality and levels

Implementing technological solutions enhances the precision, efficiency, and security of DEF management.

Dedicated DEF quality sensors can be integrated into the DEF storage and dispensing systems to continuously monitor fluid quality.

Telematics systems, when integrated with DEF systems, enable remote monitoring and management of DEF-related parameters. RFID technology can be used for secure and automated authentication in DEF dispensing systems.

Scheduled maintenance tips for DEF systems

  • Regularly check DEF levels to prevent running the system on low DEF, which can lead to inefficient emission control. Implement a routine for checking DEF levels, especially before long trips.
  • Check for any visible leaks, damage, or signs of contamination in the DEF storage tank, dispensing equipment, and associated components.
  • Follow manufacturer recommendations for filter replacement, which is usually recommended at monthly intervals.
  • Conduct a comprehensive inspection of the SCR system annually. Address any visible wear, damage, or corrosion.
  • Use dedicated equipment for DEF to prevent cross-contamination with other fluids.

Training for operators and maintenance staff on DEF handling

  • Demonstrate correct DEF dispensing procedures, including the use of clean dispensing equipment and avoiding cross-contamination with other fluids.
  • Provide hands-on training on DEF quality testing methods, such as test strips or sensors.
  • Conduct training sessions on routine maintenance tasks, including filter replacements and sensor calibrations.
  • Familiarize operators with dashboard indicators related to DEF systems and conduct practical exercises to simulate response scenarios.
  • Establish clear protocols for handling DEF spills or leaks and conduct practical training sessions.
  • Encourage participation in additional training sessions and provide resources for self-directed learning.

Dispensing Equipment and Maintenance

Here’s an overview of dedicated dispensing equipment for DEF and maintenance procedures you ought to follow to prevent diesel exhaust fluid problems from arising.

Types of DEF Dispensers

Portable DEF dispensers

These are compact, mobile units designed for flexibility in DEF distribution. They often come with wheels for easy maneuverability and are suitable for smaller-scale operations. They are typically equipped with a hose or nozzle for manual dispensing.

Fixed Tank Systems

Fixed tank systems are stationary and permanently installed, ranging from small to large tanks. They include additional features like level sensors and monitoring systems, providing a centralized and efficient solution for DEF storage and dispensing.

Automated DEF Dispensers 

These dispensers are equipped with automated dispensing with minimal user intervention and can be integrated with fleet management systems for real time monitoring. They also have features like RFID authentication and data logging, for enhanced security and control.

Maintenance and Calibration

For maintaining DEF dispensing equipment:

  • Regularly clean DEF dispensing equipment to prevent contamination, using non-abrasive materials.
  • Conduct visual inspections for leaks regularly and address leaks promptly to prevent DEF wastage and potential contamination. 
  • Replace damaged seals promptly.

Calibration ensures accurate dosing of DEF, preventing over-dispensing or under-dispensing. To perform calibration, use the following steps:

  1. Empty the dispenser.
  2. Verify current calibration settings and note any error.
  3. Dispense a known quantity of DEF using the dispenser.
  4. Use calibrated measuring equipment to determine the actual quantity dispensed.
  5. If there is a variance, adjust the dispenser's calibration settings accordingly.
  6. Repeat the test dispense and measurement to confirm accurate calibration.

You can also seek professional help for increased accuracy, especially for complex or automated dispensing systems.

Technological Advancements in DEF Systems

diesel def system problems

Integration of smart technologies into DEF dispensers has enabled fleet managers to track DEF consumption, monitor dispenser status, and receive alerts for maintenance needs, contributing to more efficient fleet management.

Advancements in automated and robotic DEF dispensing systems reduces the risk of contamination, ensures accurate dosing, and enhances safety by minimizing manual intervention.

Further integration of DEF systems with vehicle telematics allows real-time monitoring of DEF levels, quality, and dispenser status,

Research and development in nanotechnology can allow the optimization of SCR systems, potentially reducing the overall amount of DEF needed for emissions control.

As technology continues to advance, the DEF delivery systems are likely to become more sophisticated, efficient, and integrated with broader fleet management ecosystems. 


The efficient operation of modern diesel engines relies significantly on the proper management of Diesel Exhaust Fluid (DEF). From preventing freezing in cold climates to avoiding cross-contamination with the diesel tank, every aspect of DEF management contributes to the prevention of diesel exhaust fluid problems.

The risks associated with using low-quality DEF, such as corrosion, clogging, and increased emissions, underscore the need for vigilance in selecting, storing, and dispensing DEF.

For comprehensive DEF delivery services that align with best practices, explore Fuel Logic's DEF Delivery Services or find a reliable source for Bulk DEF Delivery Near You

FAQs (Frequently Asked Questions)

What are the signs of contaminated DEF and how can it be avoided?

Contaminated Diesel Exhaust Fluid (DEF) may exhibit discoloration, unpleasant odor, or unusual consistency. To prevent contamination, store DEF in dedicated containers, use clean dispensing equipment, and avoid exposing it to foreign substances.

Can DEF freeze, and what should be done if it does?

Yes, DEF can freeze in cold temperatures. However, it doesn't damage the fluid. Thawing occurs naturally, and the solution remains effective. It's crucial to ensure the DEF tank is not overfilled to accommodate expansion during freezing.

How often should DEF levels be checked in diesel engines?

Regularly check DEF levels during routine maintenance, typically aligning with oil changes. Most vehicles have a DEF gauge, but manual checks ensure timely refilling and prevent unexpected issues.

Is it harmful to mix DEF with diesel, and what should one do if this happens?

Mixing DEF with diesel is harmful and can damage the engine. If accidentally mixed, do not start the engine, drain the tank, flush the system, and refill with pure DEF.

How long can DEF be stored without losing its effectiveness?

DEF has a shelf life of about two years when stored in proper conditions: between 12°F and 86°F (-11°C to 30°C). 

Are there specific types of containers recommended for DEF storage?

Containers made of high density poly-ethene (HDPE) or materials with resistance to contamination are most suitable for the efficient storage of Diesel exhaust fluid. 

What happens if your DEF system fails?

A DEF system failure triggers a vehicle's engine derating, reducing power and speed. Immediate attention is crucial to diagnose and rectify the issue, ensuring compliance with emission standards.

What steps should be taken if the DEF indicator light comes on?

When the DEF indicator light illuminates, refill the DEF tank promptly. Ignoring the warning can lead to engine derating and potential damage.

Are there environmental concerns associated with using DEF?

DEF is a non-toxic, biodegradable solution that poses minimal environmental risks. However, spill containment measures should be in place during handling to prevent soil or water contamination.

How do I dispose of old or unused DEF?

DEF can be disposed of in water since it is biodegradable, but it’s best to visit the local recycling center or consult regulatory guidelines to ensure proper disposal in an environmentally responsible manner.

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