EPA removes DEF sensor requirement on diesel engines

After nearly two months of analyzing engine OEM data, the Environmental Protection Agency has identified inaccurate Diesel Exhaust Fluid (DEF) sensors, also known as UQS (Urea Quality Sensors), as a major impediment to uptime for truck and farm equipment operators. The analysis of warranty claims and DEF-related inducements, requested in early February, led the EPA to believe DEF sensor failures are a significant source of derates and lost productivity.

The agency informed engine manufacturers on March 26 that existing regulations allow them to use the Nitrous Oxides (NOx) sensor as alternate way to detect emissions efficiency downstream, and thus, infer poor DEF quality. Proper urea concentration in DEF is 32.5%. Software updates and augmentations to the DEF monitoring system to align with the new guidance will not violate Clean Air Act anti-tampering provision, the EPA noted.

OEMs will now be tasked with making adjustments to allow the NOx sensor replace the DEF sensor’s role in detecting poor DEF quality, or when it fails to remove NOx. This method will still allow the system to identify if an operator is watering down the DEF concentration. The EPA noted, “In most applications, NOX sensors have been able to detect poor DEF quality for many, but not all, DEF dilution scenarios.”

The EPA also said that OEMs can ask “to exclude a parameter that is difficult to access if it cannot be adjusted in a way that affects emissions without significantly degrading engine performance.”

The EPA will continue to analyze the data as more comes in. Due to the tight deadline and amount of data asked for, three of the 14 OEMs did not have enough time to fulfill the request in time, the EPA said.

The EPA asserted in the release that the move “does not weaken or remove emissions standards.”  The data suggests more often than not, the Selective Catalyst Reduction System and urea quality could be working fine, but the persnickety sensor acts as an unreliable witness and puts the vehicle in limp mode anyways.  For example, the EPA noted UQS can inaccurately detect a problem if the DEF tank has “excessive bubbles.”

For farmers or trucking fleet, sudden loss of power means the job doesn’t get done as fast as it should, and the businesses suffer. The EPA maintains that billions of dollars are lost due to subsequent repair costs and productivity losses. The U.S. Small Business Administration estimated that farmers will save $4.4 billion a year, and $13.79 billion for U.S. overall, once the guidance is implemented.

EPA Administrator Lee Zeldin called the epidemic of failing DEF system a “nationwide disaster” and asserted that truck drivers and farmers across the U.S. have asked for a change.

“Americans are justified in being fed up with failing DEF system issues. EPA understands this is a massive issue and has been doing everything in our statutory power to address this,” Zeldin stated on March 27. “Today, we take another step in furthering our work by removing DEF sensors. Farmers and truckers should not be losing billions of dollars because of repair costs or days lost on the job.” 

Zeldin’s crusade against DEF failures started last August, with the issuance of new guidance to get OEMs to change when an engine derates after detecting an issue. This provides far more time to get equipment fixed, while reducing the severity of derates over that warning period. The EPA’s ultimate goal is to remove DEF-related derates altogether.

Industry response

The American Trucking Associations noted the removal of DEF sensor requirements will add flexibility and reduce downtime, calling it a “pragmatic solution”.

Patrick Kelly, ATA VP of Energy & Environmental Affairs, stated:

“As we have previously said, these systems have too often sidelined otherwise safe, compliant trucks due to faulty or unreliable DEF quality sensors, an issue that was compounded by widespread parts shortages in recent years. When a bad sensor can trigger a full inducement, the result is unnecessary downtime, unnecessary towing costs, strained supply chains, and higher costs across the board.”

The Owner-Operator Independent Drivers Association also applauded the change. Todd Soencer, Presidnet and CEO of OOIDA, stated:

“Small-business truckers have dealt with faulty diesel exhaust fluid systems for years, facing unexpected shutdowns and costly repairs that needlessly take trucks off the road. These are serious operational and safety concerns. We appreciate EPA Administrator Zeldin for listening to the concerns of America’s truckers and issuing commonsense guidance that keeps our supply chain moving.” 

What do you think?