NOx Catalyst Efficiency Below Threshold (Bank 1)
The SCR catalyst on bank 1 is no longer reducing NOx to the level the ECU expects, even with proper reductant dosing and quality. Often the result of catalyst poisoning by sulphur or hydrocarbons, thermal aging, or a leak between the upstream and downstream NOx sensors.
Affected components
- Scr catalyst
- Nox sensor upstream
- Nox sensor downstream
Common causes
- High likelihood: SCR catalyst aged or poisoned
- Medium likelihood: NOx sensor drift
- Low likelihood: Exhaust leak between upstream and downstream NOx sensors
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
- A drive cycle may be required after repair
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.