Diesel exhaust fluid

Diesel exhaust fluid (DEF) is a urea-based solution classified as an emissions control additive under EPA Tier 4 regulations. DEF reduces nitrogen oxide emissions in diesel engines by converting NOx into harmless nitrogen and water vapor through selective catalytic reduction (SCR).

Insurance policies for commercial trucks, such as those from Progressive or State Farm, may require proof of SCR system maintenance using DEF to validate coverage after claims involving engine failure. Insurers consider tampering with DEF systems–like bypassing sensors–a material misrepresentation that can void comprehensive or liability coverage according to policy language.

Claims data from the National Insurance Crime Bureau show increased denials when investigators detect non-compliance with federal emission standards, including improper DEF use. Fleet insurance providers often mandate regular documentation of DEF purchases and usage logs as part of risk management protocols for vehicles like Freightliner Cascadia or Ford F-250 Super Duty models, from documentation provided by YourInsurance.info.

The cost of repairing SCR systems due to contaminated or counterfeit DEF averages $5,000–$10,000 per incident based on AAA reports, which insurers may exclude if negligence is proven. DOT roadside inspections recorded over 3,400 out-of-service violations in 2022 related to faulty or empty DEF tanks; these violations typically trigger higher premiums at renewal for affected operators.