EPA Allows NOx Sensors to Replace Faulty DEF Monitors on Trucks

Key Details The EPA announced new guidance allowing diesel engine manufacturers to replace problematic DEF sensors with NOx-based monitoring systems. This change bypasses the lengthy rulemaking process by using guidance rather than formal regulations. Manufacturers can now remove traditional Urea Quality Sensors and switch to alternative technology to reduce false failure alerts. Why It Matters DEF sensor failures have caused widespread frustration among truckers, triggering sudden derates that limit vehicles to speeds as low as 5 mph. These unexpected shutdowns compromise safety and productivity while stranding drivers and impacting operations. The preliminary data from 11 of 14 manufacturers confirmed DEF sensor failures are a major source of warranty claims. What's Next Starting with model year 2027, all new diesel on-road trucks must be engineered to prevent sudden severe power loss when DEF runs out. Manufacturers have already begun deploying new software in some existing vehicles to address these issues. This represents the Trump administration's ongoing effort to reduce unnecessary derates while maintaining emissions compliance standards.