DEF Testing: Data interpretation

What is DEF?

Diesel Exhaust Fluid (commonly referred to as DEF) is a liquid formulated to reduce the amount of air pollution created by a diesel engine. DEF works in a selective catalytic reduction (SCR) system to reduce the concentration of nitrogen oxides in diesel exhaust emissions.

% Urea Testing

DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. A % urea test is run to determine if there is too much or too little water within the DEF solution.

• Typical % Urea = 32.5% +/- 0.7
• If % Urea is less than: 31.8%
  • What does this mean:
    • The DEF contains too much water (i.e. the DEF is diluted)
  • Causes:
    • Quality issues within the production or blending of DEF fluids
    • Addition of straight water to the DEF (mistakenly or on purpose)  
  • Effects
    • Exhaust / emissions components will not operate as efficiently
    • This may lead to an engine fault code which may need to be cleared
  • What you should do
    • Respond to all fault codes as needed
    • Always use DEF at the proper concentration
    • Investigate potential reasons for the diluted DEF
• If % Urea is more than : 33.2%
  • Causes
    • Quality issues within the production or blending of DEF fluids
    • Evaporation of water during storage
    • Addition of concentrated urea to the DEF (mistakenly or on purpose)  
  • Effects
    • Exhaust / emissions components will not operate as efficiently
    • This may lead to an engine fault code which may need to be cleared
  • What you should do
    • Respond to all fault codes as needed
    • Always use DEF at the proper concentration
    • Investigate potential reasons for the diluted DEF

ISO Particle Count (PISO Method)

• What is this?
  • The ISO Particle Count measures the cleanliness of the DEF fluid. Particles are counted at three different size ranges (first value = >4 microns / second value = >6 microns / third value = >14 microns). Data is reported as a 3-code value. Only the second value (>6 microns) count is used for flagging  
• Typical Particle Count: less than 20/17/14
• MIN: N/A
• MAX:
  • R > 20/17/14
  • U > 21/18/15
  • S > 22/19/16
  • If ISO Particle Count is more than 20/17/14
    • Causes: Contamination can build up in DEF during storage, delivery, and transfer. DEF tanks and transfer containers that haven’t been used for some time may have excessive contamination.  
    • Effects: Contamination may result in premature wear on DEF system components including pumps or seals
    • What you should do: Ensure DEF meets cleanliness standards prior to use. Investigate the cleanliness of DEF at different stages (i.e. purchased from supplier, storage on site, in the DEF tank, etc.) and filter fluids appropriate.

Additional Resources

Page: DEF Testing and Analysis
Blog: DEF Specifications: ISO 22241
Blog: Accidents Happen: Detecting DEF Contamination Using Oil Analysis