P22FF — SCR NOx Catalyst Inlet Temperature Too Low
The temperature sensor at the SCR catalyst inlet reports a value below the threshold needed for efficient ammonia conversion. Below roughly 180-200 °C the SCR cannot reduce NOx and reductant injection is suspended; if this is detected continuously the ECU sets the fault.
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
- Scr inlet temperature sensor
- Scr catalyst
- Exhaust heat management
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Temperature sensor drifts low or has shifted resistance
- Short-trip operation - exhaust never reaches operating temperature
- Exhaust heater or heat-management strategy not active
Possible symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
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.