P22FA — NOx Sensor Performance - Slow Response High to Low (Bank 1 Sensor 1)
NOx sensor on bank 1 sensor 1 responds too slowly when NOx concentration falls (typically observed when SCR dosing increases). The sensor has aged or its protection cap is clogged.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Nox sensor
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Sensor aged
- Sensor element aged beyond calibration window
- Sensor element contaminated by oil, soot or coolant
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
Related codes
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
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.