P2001

NOx Adsorber Efficiency Below Threshold Bank 2

Q: 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.

Q: 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.

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.

Real-world scan data

Seen in

106

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Appears alongside · share of P2001 scans

P2000in 48.1% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P2001 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX