What it means
The ECM detects that the conversion efficiency of the second SCR catalyst on bank 1 is below the calibrated threshold. NOx slip past catalyst 2 is too high.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The second SCR catalyst on bank 1 treats nitrogen oxides in the exhaust using injected reductant such as DEF. The engine control module compares upstream and downstream NOx measurements to assess this catalyst's conversion efficiency. This code means NOx slip past bank 1 catalyst 2 is above the calibrated limit; it does not by itself prove the catalyst has failed.
Common causes
Most likely first.
- SCR catalyst deterioration or contamination
- Reductant dosing or quality problem
- Faulty NOx sensor or exhaust leak
Symptoms
- Check engine or emissions warning light
- Possible reduced engine power or torque limitation
How to diagnose it
- Read freeze-frame data and all SCR, reductant, and NOx sensor codes to identify the conditions and related faults present when bank 1 catalyst 2 efficiency fell below threshold.
- Inspect the exhaust around bank 1 catalyst 2 and its NOx sensors for leaks, loose joints, or damaged wiring that could distort the readings.
- Check reductant level and quality using the vehicle's specified method, and review dosing faults or warnings.
- With a scan tool, compare upstream and downstream NOx readings and catalyst temperature data under the manufacturer's prescribed conditions.
- Test the reductant dosing system, NOx sensors, and bank 1 catalyst 2 performance against the manufacturer's specification before condemning the catalyst.
Common fixes
- Repair exhaust leaks near bank 1 catalyst 2 or its NOx sensors.
- Correct reductant quality or dosing problems affecting SCR operation.
- Repair wiring or replace a NOx sensor confirmed faulty by testing.
- Replace bank 1 SCR catalyst 2 if tests confirm its conversion efficiency is below specification.
Can I keep driving?
Limit unnecessary driving and have the emissions fault diagnosed promptly, especially if a power or torque limitation appears. Continued operation can increase NOx emissions and may lead to stronger inducements or reduced power.
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.