The contact owns a 2018 Mercedes Benz Sprinter 3500. The contact stated that while starting the vehicle, the contact noticed that the Diesel Exhaust Fluid (DEF) warning light was illuminated. The vehicle was taken to the dealer where it was diagnosed and determined that the Diesel Exhaust Fluid (DEF) tank had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure and referred the contact to the NHSTA Hotline for assistance. The approximate failure mileage was 15,000.