Service Update - In some vehicles, equipped with diesel engines, the Diesel Exhaust Fluid (DEF) system may not immediately reactivate, as it should, after the vehicle?s control system finds that a DEF heater fault is no longer present. In these vehicles, after such a fault is detected as absent, DEF system reactivation, including DEF injection, may not occur until the ignition key is cycled. Dealers are to reprogram the reductant control module.