P20EE: SCR NOx Catalyst Efficiency Below Threshold
17 vehicles · 11 makes · $200-$4,500 repair
Most Reported On
P20EE is an OBD-II diagnostic trouble code meaning “SCR NOx Catalyst Efficiency Below Threshold.” This is a diesel emissions code meaning the Selective Catalytic Reduction (SCR) catalyst on Bank 1 is not cleaning up exhaust as well as it should. The SCR system sprays Diesel Exhaust Fluid (DEF) into the hot exhaust to convert harmful nitrogen oxides (NOx) into harmless nitrogen and water; NOx sensors before and after the catalyst tell the computer how well it is working. When the measured efficiency falls below the required threshold, this code sets. Because it is an emissions-protection code, it often triggers warning lights and can lead to reduced power or a speed limit (a 'derate') if left unfixed. This code is most commonly reported on 2013-2025 RAM 2500 (Big Horn, Laramie, Laramie Longhorn, Limited, Limited Longhorn, Lone Star, Rebel, SLT, Tradesman), 2014-2025 Mercedes-Benz Sprinter (Sprinter 1500, Sprinter 2500, Sprinter 3500, Sprinter 4500), and 2015-2022 Ford F-250 Super Duty, plus 14 other vehicles, with repair costs ranging from $200 to $4,500.
Common Causes
Typical Repair Cost
Based on 18 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
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 (17)
FAQ
What does P20EE mean?
P20EE stands for "SCR NOx Catalyst Efficiency Below Threshold." This is a diesel emissions code meaning the Selective Catalytic Reduction (SCR) catalyst on Bank 1 is not cleaning up exhaust as well as it should. The SCR system sprays Diesel Exhaust Fluid (DEF) into the hot exhaust to convert harmful nitrogen oxides (NOx) into harmless nitrogen and water; NOx sensors before and after the catalyst tell the computer how well it is working. When the measured efficiency falls below the required threshold, this code sets. Because it is an emissions-protection code, it often triggers warning lights and can lead to reduced power or a speed limit (a 'derate') if left unfixed.
What are the most common causes of P20EE?
The most common causes of P20EE are: Poor quality, contaminated, or wrong DEF fluid, Faulty or clogged DEF injector/dosing valve, Failed upstream or downstream NOx sensor, Degraded or failed SCR catalyst, Exhaust gas temperature sensor fault affecting dosing, Exhaust or DEF line leak, DEF line/heater problems (crystallization or freezing). The specific cause varies by vehicle.
How much does it cost to fix P20EE?
Repair costs for P20EE range from $200 to $4,500, depending on the vehicle and root cause.
Which vehicles are affected by P20EE?
Au7o has documented P20EE across 17 vehicle models from 11 manufacturers: Audi, Chevrolet, Dacia, Ford, GMC, Genesis, Land Rover, Mercedes-Benz, Opel, Peugeot, RAM.
Sources (12)
- ForumCummins Forum: SCR gone bad
- ForumRamForumz: DEF issue
- mediaTruck Camper Adventure: Going Into the Dreaded Diesel DEF Limp Mode
- manufacturerBSBuilt: Maintain 6.7L Cummins DEF System (2010-2025)
- ForumRamForumz: P2048 5 MPH Derate Def system problem
- ForumThe Diesel Stop - P207F DEF Quality Code Discussions
- articleNuDef - Ford Powerstroke DEF Problems: Causes, Codes and Fixes
- NHTSANHTSA Complaint #11376453
- ForumNOX sensor question - SilveradoSierra
- articleMercedes AdBlue Delete - Fix No-Start & Countdown Issues (Stoke Tuning)
- ForumW447 V-Class AdBlue Countdown Reset - autogmt.com
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.