P2001
NOx Adsorber Efficiency Below Threshold Bank 2
Emissions (NOx after-treatment)
Generic OBD-II
Medium
What it means
P2001 means the NOx adsorber (lean NOx trap) on bank 2 isn't capturing enough nitrogen-oxide emissions to meet the required threshold. The engine still runs and starts normally, but the vehicle is polluting more than allowed. The cause is often a worn trap or a faulty NOx sensor, and on some diesels an unresolved fault can trigger a power derate.
Medium
Can I keep driving? The car drives normally, but it's polluting more than allowed and will fail emissions — some diesels eventually derate power, so don't ignore it.
Common symptoms
What you'll notice
- Check-engine light on
- Fails an emissions / smog test
- Higher tailpipe NOx (may smell or show as haze under load)
- Reduced power if the vehicle enters an emissions derate
Common causes
Most likely first
- Aged or degraded NOx adsorber (lean NOx trap) on bank 2 no longer storing NOx effectivelyLikely
- Faulty or contaminated NOx sensor giving a low-efficiency readingCommon
- NOx sensor wiring or connector open, shorted, or corrodedCommon
- Exhaust leak near the trap or sensor skewing readingsLess often
- Underlying engine or fuel issue causing excess NOxLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for related codes (P2000, NOx sensor faults) first.
- Inspect the exhaust for leaks and the NOx sensor wiring/connector for damage.
- Verify NOx sensor readings with a scan tool; replace a faulty sensor before condemning the trap.
- If sensors and wiring are good, the NOx adsorber is likely spent and needs replacement. Clear and re-run the monitor.
FAQ
Quick answers
Is it safe to drive with P2001?+
Mechanically yes — the engine runs fine. But it's an emissions fault: you'll fail inspection and some diesels reduce power over time, so have it addressed.
Can I just clear P2001?+
It returns once the efficiency monitor runs again unless the sensor or trap is repaired. Clearing doesn't fix the underlying after-treatment problem.
Related codes
Often seen with P2001
Read & clear P2001 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX