What does P20EE mean?
The SCR (selective catalytic reduction) system injects DEF into the exhaust to turn NOx into nitrogen and water. The computer compares the NOx sensors before and after the SCR catalyst. P20EE means NOx is not dropping as much as it should.
Codes are a starting point. They tell you which test failed, not which part to replace. Check for other stored codes and fix those in a sensible order.
Symptoms
- Check engine light
- DEF or emissions warning
- Speed limit countdown on many trucks
Common causes
- Bad or diluted DEF
- Faulty NOx sensor (upstream or downstream)
- DEF injector clogged with crystals
- Weak DEF pump or low DEF pressure
- Exhaust leak near the sensors
- Worn or contaminated SCR catalyst
How to diagnose P20EE
- Test the DEF with a refractometer (should be about 32.5% urea).
- Check NOx sensor readings with a capable scan tool.
- Inspect the DEF injector for crystals and check the spray pattern if your tool can run the test.
- Check for exhaust leaks.
- Look up software updates and extended warranty coverage for your truck.
How to fix it
- Drain and refill with fresh DEF
- Replace the faulty NOx sensor
- Clean or replace the DEF injector
- Repair DEF pump or lines
- Replace the SCR catalyst (last)
Estimated repair cost
Likely repairs for P20EE run from about $50 to $6,000, depending on the cause.
| Repair | Typical range (parts + labor) |
|---|---|
| Diagnostic fee (scan + testing) | $100 - $200 |
| Drain and refill DEF | $50 - $200 |
| NOx sensor replacement (one) | $400 - $1,000 |
| DEF injector (doser) | $400 - $1,200 |
| DEF pump / supply module | $700 - $1,800 |
| SCR catalyst replacement | $2,500 - $6,000 |
These are rough US estimates for an independent shop in 2026, based on typical parts prices and standard labor times. Dealers, big trucks, luxury brands and high-cost areas often run higher. They are not quotes. Use the repair cost estimator to adjust for your vehicle.
How serious is P20EE?
High severity
Get it fixed soon. Many trucks will limit speed after a countdown if the SCR fault is not fixed.
Make-specific notes
Cummins (Ram 6.7L)
P20EE is very common on 2013 and later Ram 6.7L trucks. Ram released software updates and some SCR warranty extensions; a Ram dealer can check by VIN.
Duramax (GM 6.6L)
On the LML and L5P, NOx sensors and DEF quality are frequent causes.
Powerstroke (Ford 6.7L)
On the 6.7L, check the NOx sensors and the DEF injector for crystal buildup.
Always check open recalls and technical service bulletins for your VIN.
P20EE FAQ
Will a new NOx sensor fix P20EE?
Only if a sensor is actually bad. Test the DEF quality and check the doser first, since those are cheaper.
Can bad DEF cause P20EE?
Yes. DEF that is old, diluted or contaminated does not reduce NOx properly. DEF also breaks down faster in heat.
What does P20EE mean?
P20EE stands for "SCR NOx Catalyst Efficiency Below Threshold (Bank 1)". The SCR (selective catalytic reduction) system injects DEF into the exhaust to turn NOx into nitrogen and water.
Can I drive with a P20EE code?
Get it fixed soon. Many trucks will limit speed after a countdown if the SCR fault is not fixed.
How much does it cost to fix P20EE?
It depends on the cause. The likely repairs for P20EE range from about $50 to $6,000 at an independent shop in the US, plus a diagnostic fee of roughly $100-$200. These are rough estimates; dealer prices and some vehicles run higher.
What is the most common cause of P20EE?
The most common causes are: bad or diluted DEF; faulty NOx sensor (upstream or downstream); dEF injector clogged with crystals.