While it seems hard to believe, a device less than two feet tall and weighing only 5 lb. enables truck drivers to transport freight across America efficiently.

America’s more than 3.5 million truck drivers are not only essential to the nation’s supply chain but are also a major economic growth engine. The trucking industry directly contributes approximately 5% of overall U.S. GDP. It moves more than 70% of the nation’s freight by weight, with volumes expected to grow through 2030 given the sustained uptick in the movement of goods across the country.

Diesel Exhaust Fluid (DEF) headers, inside a truck’s DEF tank, house critical sensors that make all of this possible.

Despite being carefully integrated into a vehicle’s emission control system, the Environmental Protection Agency (EPA) recently issued guidance reminding manufacturers that DEF-sensing urea quality sensors are optional. This guidance was based on a partial data set spanning more than a decade and the EPA’s discussions with truck drivers, farmers, and other operators about frustrations with DEF systems. The EPA noted that operators can instead use nitrogen oxide (NOx) sensors alone to comply with the EPA’s NOx emissions standards.

Like many Americans, truck drivers are navigating rising fuel prices, higher costs at the supermarket, and increasing health insurance premiums. The last thing they need are regulations that will actually make it more difficult and more expensive to do their jobs.

Understanding the role of DEF in SCR performance

DEF systems are essential to the selective catalytic reduction (SCR) process in diesel vehicles, which uses chemical reactions to neutralize NOx emissions. DEF headers specifically monitor the DEF fluid level, temperature, and quality to help comply with stringent NOx emissions standards.

While NOx sensors are part of the SCR process, they most often work in tandem with urea quality sensors to accurately track DEF quality and NOx emissions. NOx sensors measure the NOx levels in the exhaust exiting the vehicle’s tailpipe but cannot measure DEF quality or track how much of it is being used. NOx sensors alone cannot optimize DEF dosing because they cannot track DEF concentration and lack the feed-forward control required to spray the ideal amount of DEF at each stage of the SCR process.

Like diesel fuel, DEF is an expense for truck drivers, and its usage must be carefully managed to avoid wasting money. Given the choice, why would a truck driver forfeit a system designed to optimize costly fluid consumption while avoiding financial penalties associated with failing to conform to emissions regulations?

The operational risks of removing DEF sensors

The EPA’s common-sense approach to regulation and focus on driving economic growth has the potential to further improve the current operating environment, but removing DEF quality sensors from trucks and other diesel equipment would negatively impact truck drivers. It could threaten the longevity of their vehicles.

Over the last decade, American DEF system manufacturers have worked closely with many well-known original equipment manufacturers (OEMs) to improve the performance of legacy DEF systems. Together, OEMs and their suppliers continue adjusting to evolving regulations, successfully extending the useful life of sensor equipment exposed to DEF and reducing false DEF sensor readings. Longer component service life, in addition to a typical 2-3% fuel efficiency improvement, has helped equipment operators lower operating costs with the latest-generation equipment.    

What’s more, a proliferation of multiple engine management systems within a single vehicle manufacturer increases complexity and, ultimately, costs for consumers. Let’s remember that manufacturers reduce costs in part by leveraging scale.

The California Air Resources Board (CARB)-following states and the European Union, which are massive truck markets for OEMs, have very strict NOx emissions requirements and have no plans to change course, so it’s not economically feasible for vehicle manufacturers to change engine system architecture to follow the EPA’s evolving requirements while others continue to tighten them.

Bottom-line impact: Efficiency and economic stability

DEF systems ensure diesel equipment complies with clean air regulations while saving truck drivers money at the pump. America’s DEF system manufacturers have worked tirelessly with leading OEM partners to increase system reliability and reduce downtime for truck operators with several follow-on economic benefits.

The EPA’s current DEF regulations and recent engine inducement revisions strike a practical balance between increasing productivity, promoting economic growth, and complying with emissions regulations. Truckers are the foundation of our national economy, and we encourage the EPA to continue its common-sense approach to regulation, so that truckers can continue to do their jobs and keep our economy moving.