P20F2: SCR NOx Catalyst Efficiency Below Threshold (Bank 2)
SCR NOx Catalyst Efficiency Below Threshold (Bank 2): the control module has detected this fault condition.
What P20F2 means
P20F2 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 2 is the side of a V or flat engine opposite cylinder 1.
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Yes
- Drive cycle to clear
- Required
Get it fixed
Post this code once and get quotes from local mechanics. Free to post.
Makes the repair and parts links below specific to your car. Kept in this browser only.
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 thermally agedMost likely
- 02Catalyst poisoning from sulphur or oil ashPossible
Can I drive with P20F2?
Not recommended beyond getting it to a shop.
This fault can put the engine or transmission in limp mode with reduced power, which can make merging and passing unsafe. Have it diagnosed as soon as possible.
Why we rate it urgent
- Can put the vehicle in limp mode (reduced power)
- 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 P20F2
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P20F2. 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 thermally aged; catalyst poisoning from sulphur or oil ash. 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.
P20F2 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 downstream
P20F2 FAQ
What does P20F2 mean?
P20F2 means “SCR NOx Catalyst Efficiency Below Threshold (Bank 2)”. SCR NOx Catalyst Efficiency Below Threshold (Bank 2): the control module has detected this fault condition.
Is P20F2 serious? Can I keep driving?
We rate P20F2 as urgent severity. Not recommended beyond getting it to a shop. This fault can put the engine or transmission in limp mode with reduced power, which can make merging and passing unsafe. Have it diagnosed as soon as possible.
What causes P20F2?
The most common causes, from most to least likely: SCR catalyst thermally aged; Catalyst poisoning from sulphur or oil ash. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P20F2?
Typical labor is about $250–$1,000 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 P20F2 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 P20F2 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.