DEF: A Must - Have For Truckers On The Road - Everything You Need To Know!

For truck drivers who spend years hitting the road to make a living, Diesel Exhaust Fluid (DEF) is an absolute necessity for daily operations. Its usage keeps rising with each passing day – without it, your vehicle won't just fail emission standards, but may even face speed and torque restrictions, seriously disrupting your work. Today, we’re breaking down all the key facts about DEF that every trucker should know!

What Is DEF?

Diesel Exhaust Fluid (DEF), also commonly known as automotive urea, vehicle urea, automotive environmental urea, or diesel vehicle exhaust purification fluid, is a transparent, colorless liquid mainly composed of urea and deionized water. DEF is usually stored in a dedicated fluid tank on the vehicle and used in SCR (Selective Catalytic Reduction) technology.

Key Standards for DEF

The standards for DEF mainly cover the following aspects:

1. Concentration: The concentration of DEF is generally around 32.5%. According to GB/T 29518, the concentration must be between 31.8% and 33.2%. This concentration refers to the mass percentage of urea in the solution.

2. Density: Under the standard temperature of 20°C specified in GB/T 29518, the standard density of DEF should be controlled within the range of 1087.0 to 1093.0 kg/m³ (i.e., 1.0870 to 1.0930 g/cm³).

3. Moisture Content: The moisture content of DEF should be between 0.3% and 1.0%.

4. Total Nitrogen Content: The total nitrogen content of DEF (on a dry basis) should be greater than 46.3%.

5. Biuret Content: The biuret content in DEF should be less than 0.5%.

6. Iron Content: The iron content in DEF (calculated as Fe) should be less than 0.0005%.

7. Alkalinity: The alkalinity of DEF (calculated as NH₃) should be between 0.01 and 0.03.

In addition, DEF must meet other requirements, such as:

Appearance: It should be a colorless, transparent, and clear liquid.

Odor: It should have no obvious unusual smell.

pH Value: It should be between 4.5 and 8.5.

In the exhaust treatment system of diesel vehicles, especially those using SCR technology, DEF is injected into the exhaust pipe. Under high-temperature conditions, urea decomposes into ammonia. Subsequently, ammonia reacts with nitrogen oxides (NOₓ) in the exhaust gas under the action of an SCR catalyst, reducing NOₓ to nitrogen (N₂) and water (H₂O). This process reduces NOₓ emissions, minimizes environmental pollution, optimizes engine performance and fuel consumption, lowers diesel usage, and enhances the vehicle's environmental friendliness.

How to Identify Qualified DEF? Remember These 4 Tips!

There are many brands of DEF on the market, but their quality varies. Substandard DEF can trigger fault alarms and, over time, damage the engine's after-treatment system.

Check the Appearance & Packaging: Ensure no damage and avoid "three-no" products (no brand, no standard, no manufacturer).

For bottled DEF, check if the packaging is intact and undamaged. Verify that the product name, trademark, and barcode on the bottle label are clear, and check the shelf life-expired DEF can only be used after testing. High-quality DEF is transparent, pure, and has a faint blue tint. Products that are yellow, turbid, or contain impurities/foreign objects are substandard and should be used with caution. The engine’s DEF quality sensor in the DEF tank will trigger relevant fault codes if the DEF quality is unqualified or the fluid level is low.

Smell the Odor: Unusual smells indicate substandard products.

Freshly produced DEF is odorless. However, after exposure to high temperatures, sunlight, or prolonged storage, a small amount of urea decomposes into ammonia, resulting in a faint ammonia smell. DEF with a pungent or unusual odor is likely substandard.

Monitor System Self-Checks: Replace DEF promptly if the system alarms.

Through the engine's DEF quality sensor in the DEF tank, the system will trigger fault codes if the DEF quality is unqualified or the fluid level is low.

Use a Refractometer: Test DEF concentration with professional equipment.

A refractometer can be used to measure the concentration of DEF, helping to determine its quality.