What it means
The module determines that the SCR NOx pre-catalyst on bank 1 is not reducing nitrogen oxides as effectively as expected. It sets the code when the monitored conversion efficiency falls below the calibrated threshold.
How it works
The SCR pre-catalyst is the upstream NOx conversion stage in bank 1's aftertreatment system. The module uses NOx sensor readings and operating data to estimate how much nitrogen oxide this stage removes. This code sets when the bank 1 pre-catalyst's monitored efficiency is below its calibrated threshold.
Common causes
Most likely first.
- Damaged or degraded SCR pre-catalyst
- Faulty NOx sensor
- Incorrect or contaminated reductant
- Reductant dosing fault
- Exhaust leak
Symptoms
- Check engine light
- Reduced engine power
- AdBlue or emissions warning
- Possible starting restriction warning
How to diagnose it
- Review freeze-frame data and live NOx readings associated with the bank 1 pre-catalyst to see when the efficiency monitor failed.
- Check for related reductant, NOx-sensor, exhaust-temperature, and dosing codes that may explain the low efficiency.
- Inspect the bank 1 exhaust joints around the pre-catalyst and NOx sensors for leaks that can affect readings or treatment.
- Check the bank 1 NOx sensor wiring and connectors, then compare live readings for plausibility during stable operation.
- Verify reductant condition and dosing against the manufacturer's specification and assess pre-catalyst conversion before replacing components.
Common fixes
- Repair exhaust leaks affecting the bank 1 pre-catalyst or NOx measurements.
- Repair wiring or connectors at the affected bank 1 NOx sensor.
- Replace a NOx sensor confirmed inaccurate by testing.
- Correct contaminated reductant or a dosing fault identified during checks.
- Replace the bank 1 SCR pre-catalyst if its conversion remains below specification after other faults are corrected.
Can I keep driving?
Drive only as needed and avoid heavy loads if power is reduced; continued operation may worsen emissions and can lead to an emissions or starting restriction warning. Have the reductant and bank 1 pre-catalyst system checked promptly.
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.