What it means
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.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The SCR catalyst in bank 1 uses injected reductant to convert exhaust nitrogen oxides into less harmful gases. The module compares NOx readings before and after this catalyst to estimate how effectively it is working. This code sets when bank 1 conversion efficiency falls below the monitored threshold.
Common causes
Most likely first.
- SCR catalyst aged or poisoned
- NOx sensor drift
- Exhaust leak between upstream and downstream NOx sensors
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
How to diagnose it
- Read freeze-frame data and live upstream and downstream NOx readings for bank 1 to confirm the conditions when efficiency was judged low.
- Check for related reductant-quality, dosing, exhaust-temperature, and NOx-sensor codes before condemning the catalyst.
- Inspect the exhaust between the bank 1 upstream and downstream NOx sensors for leaks that could distort the measured conversion.
- Inspect both bank 1 NOx sensors, their connectors, and wiring; compare their live data for plausibility under stable operating conditions.
- Verify reductant quality and dosing operation against the manufacturer's specification, then assess catalyst conversion before replacing the SCR catalyst.
Common fixes
- Repair an exhaust leak between the bank 1 NOx sensors.
- Repair damaged wiring or connections to the affected bank 1 NOx sensor.
- Replace a NOx sensor confirmed to drift or report implausible readings.
- Correct a reductant quality or dosing fault if testing identifies one.
- Replace the bank 1 SCR catalyst if it fails an efficiency check after sensor, leak, and dosing faults are ruled out.
Can I keep driving?
You can usually drive gently if the engine runs normally, but arrange diagnosis soon because emissions performance is reduced and the vehicle may fail an inspection. Avoid heavy loads if a sulfur smell or power reduction develops.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.