If hydrogen is obtainable during the exhaust, the TWC/TWNSC may also create ammonia, which reduces the essential level of urea injection; It does not detect and supply an alert in just about every problem. It really is the driving force's responsibility to stay inform at all times. See Owner’s Manual https://andersonxtoga.yourkwikimage.com/651124/indicators_on_save_fuel_with_water_you_should_know