محلول المعالجة مخفف أو سائل خاطئ

The SCR tank filled with something other than fresh diesel exhaust fluid — topped up with water, stretched with it, or filled with a fluid that never was DEF. The system measures the fluid's quality, not just its level, and dilute urea cannot convert the NOx the dosing calculation expects it to; the shortfall reads as an emissions exceedence with the tank apparently full.

The fix is honest fluid: drain and refill with DEF from a sealed container meeting ISO 22241. Concentration matters (32.5% urea is the spec, not a suggestion), the fluid ages in heat and sunlight, and a bargain top-up that triggers the inducement ladder is the most expensive saving a diesel can make.