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EPA approves DEF sensor removal

  • Mercados: Fertilizers
  • 27/03/26

US diesel engines will no longer be required to have urea quality sensors (UQS) and will revert to using nitrous oxide (NOx) sensors, according to Environmental Protection Agency (EPA) guidance issued on Thursday.

That could lead to less diesel exhaust fluid (DEF) — a mixture of urea and de-ionized water, consumption in both road and non-road diesel engines — as the EPA implies a certain level of allowable dilution of urea concentration in DEF supply in special catalyst reduction (SCR) systems. An SCR system uses DEF to neutralize NOx emissions in diesel engines.

The standard concentration of urea in DEF is 32.5pc, but the concentration can be diluted further by using lower-quality DEF and leading to small increases in NOx emissions.

The agency's previous guidance to reduce inducement penalties, or engine power reductions because of SCR system faults,on users may also cut demand as users will no longer be required to carry an extra case of DEF to avoid engine derating in case of low DEF supply.

UQS can detect DEF dilution and quality, but require certain parameters to operate correctly. The EPA determined, via data from the Truck and Engine Manufacturers Association, that UQS have some of the highest failure rates of equipment across SCR systems.

As a result, the EPA on Thursday suggested that original equipment manufacturers (OEMs) return to the NOx sensors that were the main sensors present on SCR systems prior to model year 2016 road engines and model year 2017 non-road equipment.

The EPA says the fix can be done via a software update through some OEMs. The EPA, in an effort to reduce impact from DEF inducements because of faulty UQS, is encouraging OEMs to seek alternative monitoring technologies to improve robustness of SCR systems.

In guidance issued in February, the EPA also affirmed that approved NOx sensor software updates can be installed on existing engines by owner/operators without being treated as tampering under the Clean Air Act.


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