What it means
The lean NOx trap (LNT) on bank 2 is no longer storing or releasing NOx within the required efficiency window. Detected by the downstream NOx sensor or model-based monitor — typically caused by sulphur poisoning, thermal aging, or a failed regeneration strategy.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The NOx adsorber, or lean NOx trap, stores nitrogen oxides in the exhaust on bank 2 and releases them during regeneration. The control module evaluates its efficiency using downstream NOx sensor data or a model; P2001 sets when bank 2's adsorber falls below the required efficiency window, including from sulphur poisoning or thermal aging.
Common causes
Most likely first.
- Sulphur poisoning
- Thermal aging of washcoat
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Scan freeze-frame data and related emissions codes, then review bank 2 downstream NOx readings and regeneration history for the conditions linked to the fault.
- Inspect the exhaust around the bank 2 adsorber and downstream NOx sensor for leaks, loose connectors, or damaged wiring.
- Check that bank 2's regeneration strategy is operating as specified and look for related control faults that could affect adsorber efficiency.
- Compare bank 2 downstream NOx sensor behavior with the manufacturer's specification and, where available, data from the other bank.
- If the sensor, exhaust, and regeneration checks pass, assess the bank 2 adsorber for persistent efficiency loss or thermal aging.
Common fixes
- Repair exhaust leaks or damaged connections around the bank 2 adsorber and sensor.
- Correct a regeneration-control fault that prevents the specified operating strategy.
- Replace the bank 2 downstream NOx sensor if testing confirms it is faulty.
- Replace the bank 2 NOx adsorber if testing confirms persistent efficiency loss or thermal aging.
Can I keep driving?
The vehicle may remain driveable, but NOx emissions can exceed limits and the vehicle may fail inspection; an emissions warning can lead to a no-start countdown on some vehicles. Respond promptly to any countdown or emissions-system warning.
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.