NOx Exceedence — Reagent System Performance
The SCR system has detected that NOx emissions exceed the legal limit and the cause is traced to a performance fault in the reagent dosing system — for example a slow dosing pump, a clogged injector, or a frozen line that is not yet caught by another DTC.
Affected components
- Reductant dosing unit
- Reductant injector
- Reductant pump
Common causes
- High likelihood: Reductant injector clogged with crystals
- Medium likelihood: Dosing pump output below spec
- Medium likelihood: Reagent supply line blocked
Possible symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
- Reduced-power or limp mode may occur
Related codes
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.