P20EE: SCR NOx Catalyst Efficiency Below Threshold
12 vehicles · 9 makes
P20EE is an OBD-II diagnostic trouble code meaning “SCR NOx Catalyst Efficiency Below Threshold.” The selective catalytic reduction system is not reducing NOx emissions effectively. Common on diesel trucks with DEF systems. This code appears across 12 vehicle models from 9 manufacturers.
Common Causes
Diagnostic Tools
To diagnose P20EE, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
As an Amazon Associate, we earn from qualifying purchases. Prices are approximate and may vary.
Vehicles Affected (12)
FAQ
What does P20EE mean?
P20EE stands for "SCR NOx Catalyst Efficiency Below Threshold." The selective catalytic reduction system is not reducing NOx emissions effectively. Common on diesel trucks with DEF systems.
What are the most common causes of P20EE?
The most common causes of P20EE are: Poor quality DEF fluid, Failed DEF injector, Contaminated SCR catalyst, DEF quality sensor fault, Insufficient DEF dosing. The specific cause varies by vehicle.
How much does it cost to fix P20EE?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by P20EE?
Au7o has documented P20EE across 12 vehicle models from 9 manufacturers: Audi, Chevrolet, Ford, GMC, Genesis, Land Rover, Mercedes-Benz, Peugeot, RAM.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.