Poor DEF Quality Detected. Engine will Derate in 60 minutes— What’s This?

Whether you just received the poor DEF quality alert just now or sixty minutes earlier, there are no ways you can continue driving if you ignore this message. Many truck drivers have been stranded along the way after receiving and ignoring this message. These instances put business operations on hold apart from the wasted time and operation costs because of not knowing how to deal with poor DEF alerts.

Poor DEF quality detected message highlights

• Common reasons:low DEF, issues with DEF injection, bad DEF
• How to fix:add DEF, have the car inspected
• Possible consequences:engine may go to limp mode
• Priority level:High
• Can you drive?Yes
• DIY repair:Possible
• Repair price range:$50-$250

DEF and the SCR System Explained

Selective Catalytic Reduction is one of the not-so-newest emission control technology launched in 2010, where the system reduces NOx or nitrogen emissions to almost zero levels.

In this system, the engine releases hot exhaust gases that flow into the aqueous filter system, where DEF liquid gets sprayed into the specialized catalyst in the exhaust system. The sprayed DEF liquid creates a chemical reaction where exhaust gases or NOx emission converts into harmless oxygen, CO2, and nitrogen particles. It goes through a series of filters until the tailpipe releases clean emissions.

As a result, the system can reduce the following:

• NOx emissions by 90%
• HC & CO2 emissions by 50 to 90%
• PM (particulate matter) emissions by 30 to 50%

All heavy trucks released in 2011 were obliged to have SCR technology in their vehicle as imposed in new EPA emission standards.

The DEF Liquid

The Diesel Exhaust Fluid, or DEF, is a chemical solution made of 67.5 % deionized water and 32.5% urea. Urea is a substance in Nitrogen that turns into ammonia when heated and is derived technically from urine.

While there are many advantages of using DEF liquids, the SCR system and Diesel Particulate Filter (DPF) have some issues to watch out for since they tend to clog over time. It can affect the pressure and temperature in the exhaust resulting in maintenance & repair problems and performance issues.

And one of them is the Poor DEF Quality Detected screen alert.

What Does Poor DEF Quality Detected Means?

The DEF fluid is a complicated system where many functions of the engines integrate with. When it detects irregularities, it can send signals to the ECU, and the computer regulates the engine's speed to as slow as 5 mph or shut it down.

The DEF has a system with DEF sensors that measures DEF temperature, concentration, and liquid level. One sensor is the DEF quality sensor which measures the DEF concentration and detects contaminants in the DEF tank.

Poor DEF Quality detected alert is an irregularity measured in the quality of the DEF liquid or the SCR system itself. The quality of the DEF liquid influences many functions in the SCR system, but you cannot blame the DEF liquid for all cases.

Causes of Poor DEF Quality Message

Poor DEF Quality alerts arise from many situations:

DEF Quality is compromised

The SCR is a complicated design that has many advantages but also a lot of requirements to work efficiently. One of them is to have quality DEF liquid. The solution contains 67.5 % deionized water and 32.5% urea. For a DEF liquid to become good quality, it must be stored and used at optimum temperature. It must contain no other liquid or contaminants other than its composition.

When the DEF sensors detect irregularities in DEF quality, it sends the reading to the ECU prompting the engine to derate and regulate the speed of your vehicle.

• Contaminated

Your DEF liquid should be free from contaminants. DEF liquid has a clear transparent liquid. When your DEF liquid contains dirt, tank scale, or rust, it can result in abrasion in your DEF pump. These contaminants often accumulate during storage. And you don't want them to be present in your DEF tank, or it will prompt a Poor DEF quality message.

• Out of Concentration

Your DEF liquid should keep its concentration to the standard, 32.5% urea and 67.5% water. The SCR system consists of a urea quality sensor that analyzes the urea concentration. It should test for composition between 31.8 and 33.2%. Any amount more or less than preferred will result in a poor DEF quality message. Diluting it with more water will decrease the NOx neutralization properties.

• Other fluids

The DEF tank is always next to the diesel tank. Pay attention when topping up with fuel, as it is not impossible to open the DEF cap. Having other fluids present, like diesel, engine oil, or coolant, will damage your SCR and cause the engine shut down.

Cold Weather

DEF crystallizes or freezes at 12°F. Being frozen does not degrade or affect the performance of DEF liquid. It doesn't dilute. However, it will stop engine operations as the SCR system does not work with solidified DEF. You will receive a Poor DEF Quality alert on your monitor as the product is not working as a liquid.

What you can do is, let it thaw normally until it liquifies to its original state. The concentration will be the same. However, it is worth noting that you should not use anti-freeze products as they will damage the SCR system.

Faulty NOx sensors

Poor DEF Quality message does not only prompt on DEF liquid's poor quality. It can also notify when there are irregularities in the SCR system itself.

The NOx sensor measures the NOx gas concentration in diesel vehicles with an SCR system. The system relies on the signals from the NOx sensor to decide how much DEF liquid to spray. This sensor is small but costly when damaged. It can cause incorrect wiring readings and disrupt the vehicle's ECU and SCR systems.

The common causes of faulty NOx sensors are moisture contact from the exhaust or during replacement and soot build-up. So when the SCR system detects abnormal readings and signals from this sensor, it will trigger a Poor DEF quality message on your dashboard.

Contaminated SCR box

A contaminated SCR box can prompt a Poor DEF Quality alert. Any contamination should not get into your SCR box as it can cause huge costly repairs.

Coolant, fuel, and engine oil can get into your after-treatment system don't only affect its processes by its components as well. These contaminants may cause damage to the catalyst, particulate filter, and SCR filters. Cleaning or repairing these filters can cost $1500 to $5000.

Possible EGR issues

If your EGR system has issues, it can also prompt poor DEF quality detected notification in your dashboard. When there are failures in your EGR cooling system, coolant can get into the exhaust and reach the after-treatment system of your vehicle. Aside from that, if the EGR disrupts the formation of a sound air-fuel mixture, it can also damage the engine and clog your after-treatment system.

What happens when you have bad DEF quality?

• Increased DEF consumption by equipment
• Reducing DEF effectiveness
• Engine derating or shutdown
• Potential SCR component damages, including the DEF dosing pump and (DPF) diesel particulate filter
• SCR system malfunctioning

Diagnosis

Your previous trouble codes should help you diagnose a Poor DEF quality alert. You may have trouble finding the cause of the problem without any of them.

When you first receive the alert followed with Engine will derate in 60 minutes, and you know the engine will shut down soon. 

The first thing to do is to stop your vehicle and do a visual inspection. Better yet, call your service workshop for scanning.

Check your DEF tank first and check for any possible contaminants. 

If this message comes after refilling your DEF tank, you need to test the liquid. 

Go over your exhaust, DEF, EGR, and SCR systems. Look for existing leaks, crystallization, blockages, corrosion, and possible wear.

Solidified DEF accumulates over time and can happen anywhere in the SCR and exhaust system. Check for them on connections, piping, and the DEF doser.

DEF liquid should be clear. Check for the filters and your containers. Look for debris, dirt, and particles.

Meanwhile, you can test the fluid for urea concentration using a refractometer.

All these would be easy by contacting a service workshop nearby. 

If you haven't brought your truck for regular maintenance, be ready for a tune-up: DEF filters, NOx filter replacement, and EGR tune-up. It will help you reset your entire SCR system and help the ECU receive accurate readings.

What if I Accidentally Filled the DEF tank with Diesel?

Do not attempt to run your engine if you have contaminated the DEF tank with diesel.

Ask for professional help in the shop to dispose of DEF liquid safely. Never dispose of this liquid by yourself. DEF disposal requires special equipment and handling by professionals as it poses danger to the environment.

How to Keep the Good Quality of DEF?

Store your DEF liquid in DEF-approved containers. Do not place them in containers made of copper, carbon steel, or alloys containing zinc-coated steel or copper. DEF liquid is a corrosive substance. When storing DEF, keep an optimal temperature of 75 to 77°F. If the liquid has prolonged exposure to areas with over 86°F temperature, your DEF quality will decrease. With proper storage, your DEF liquid will stay at its best quality for up to two years.

Also, keep your dispensers, including the nozzles and fill points clean. Assign a member to monitor your DEF levels and these maintenance precautions to avoid future costly repairs.