OBD-II code · Powertrain (generic, extended)
P20EE NOx Catalyst Efficiency Below Threshold (Bank 1)
The SCR catalyst on bank 1 is no longer reducing NOx to the level the ECU expects, even with proper reductant dosing and quality. Often the result of catalyst poisoning by sulphur or hydrocarbons, thermal aging, or a leak between the upstream and downstream NOx sensors.
Is it safe to drive with P20EE?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelySCR catalyst aged or poisoned
- PossibleNOx sensor drift
- Less likelyExhaust leak between upstream and downstream NOx sensors
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1.5–6 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Scr Catalyst, Nox Sensor Upstream, Nox Sensor Downstream
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.