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.
What P20EE means
P20EE is a generic OBD-II powertrain code in the emissions group. In plain English: the catalytic converter is no longer cleaning the exhaust as well as it should. The computer judges this by comparing the oxygen sensors before and after the converter. Bank 1 is the side of the engine with cylinder 1 (inline engines only have bank 1).
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Required
Get it fixed
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Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Common causes
- 01SCR catalyst aged or poisonedMost likely
- 02NOx sensor driftPossible
- 03Exhaust leak between upstream and downstream NOx sensorsLess likely
Can I drive with P20EE?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
- Needs a drive cycle to confirm a repair
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P20EE
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P20EE. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Fix other faults first
If other codes are stored, start with power-supply, sensor-circuit and communication codes. They can cause this code as a side effect.
- 3
Compare upstream and downstream O2 sensors
With the engine warm, the upstream sensor should switch rapidly while the downstream one stays fairly steady. A downstream signal that mirrors the upstream one points to a worn catalyst; check for exhaust leaks and misfires first.
- 4
Test the likely causes in order
Start with the most likely cause and work down: SCR catalyst aged or poisoned; NOx sensor drift; exhaust leak between upstream and downstream NOx sensors. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and complete a full drive cycle (cold start, idle, steady highway cruise, deceleration). The code is fixed when the related readiness monitor completes without it returning.
P20EE repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Hard
- Good DIY job?
- Usually a shop job
Involved testing or major parts. Most owners use a shop.
Parts and systems involved
- SCR catalyst
- NOx sensor upstream
- NOx sensor downstream
P20EE FAQ
What does P20EE mean?
P20EE means “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 P20EE serious? Can I keep driving?
We rate P20EE as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes P20EE?
The most common causes, from most to least likely: SCR catalyst aged or poisoned; NOx sensor drift; Exhaust leak between upstream and downstream NOx sensors. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P20EE?
Typical labor is about $190–$750 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P20EE myself?
DIY difficulty is hard. Most owners leave this to a shop because it needs involved testing or specialist tools. Always confirm the cause before buying parts.
Will P20EE clear itself?
Once the fault is fixed, the check engine light usually goes off by itself after the system passes its self-test over several drive cycles. Clearing the code with a scan tool resets readiness monitors, so an inspection station may turn you away until a full drive cycle is completed.