P20EE: SCR NOx catalyst efficiency below threshold (bank 1)
The SCR catalyst, which uses AdBlue to clean up nitrogen oxides, is not performing well enough. Usually poor AdBlue, the injector or a sensor.
| Code | P20EE |
|---|---|
| System | Engine and transmission |
| Group | P20xx, Emissions: catalysts and AdBlue |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P20EE means
Many modern diesels inject AdBlue (a urea solution) into the exhaust so the SCR catalyst can turn nitrogen oxides into nitrogen and water. Two NOx sensors, before and after, check that it works. The ECU sees that more NOx than allowed is left at the outlet.
Most common causes
- Poor quality, diluted or very old AdBlue
- AdBlue injector blocked with crystals
- Faulty or drifting NOx sensor
- Exhaust leak ahead of the SCR catalyst
- Aged or damaged SCR catalyst
- AdBlue pump or lines not reaching the correct pressure
Symptoms
- Engine warning light on
- AdBlue or emissions warning on the dashboard
- Possible countdown before the engine is prevented from starting
- Usually nothing noticeable when driving
Can you drive with P20EE?
With care You can drive, but get to a garage soon. On many cars, if the fault persists, a dashboard message counts down the distance left before the engine will not restart.
Open the bonnetthe in-depth explanation
How to check it
If you topped up AdBlue recently, tell the garage where and when. On your scanner, compare the two NOx sensors: if the outlet one reads almost the same as the inlet one, the SCR is not doing its job.
How to read and clear P20EE with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P20EE with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P20EA The relay supplying the reductant control unit performs incorrectly
- P20EB The relay supplying the reductant control unit performs incorrectly
- P20EC The SCR NOx catalytic converter (bank 1) is getting too hot
- P20ED The NOx sensor before the catalyst on bank 1 is at an excessive temperature
- P20EF The NOx sensor before the catalyst on bank 1 is operating below the efficiency
- P20F0 The SCR NOx catalytic converter (bank 2) is getting too hot
- P20F1 The NOx sensor before the catalyst on bank 2 is at an excessive temperature
- P20F2 The NOx sensor at the catalyst on bank 2 is operating below the efficiency
- P2002 Diesel particulate filter efficiency below threshold (bank 1)
- P2003 Diesel particulate filter efficiency below threshold (bank 2)
- P2004 Intake manifold runner control stuck open (bank 1)
- P2005 Intake manifold runner control stuck open (bank 2)
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: AdBlue.
What does code P20EE mean?
Many modern diesels inject AdBlue (a urea solution) into the exhaust so the SCR catalyst can turn nitrogen oxides into nitrogen and water. Two NOx sensors, before and after, check that it works. The ECU sees that more NOx than allowed is left at the outlet.
Can you drive with P20EE?
You can drive, but get to a garage soon. On many cars, if the fault persists, a dashboard message counts down the distance left before the engine will not restart.
How do you clear P20EE?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P20EE comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
