Service Update (population expanded). 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.