What Does P20EE Mean?
The SCR NOx catalyst on Bank 1 is not reducing nitrogen oxide emissions to acceptable levels. The system detects that NOx conversion efficiency has fallen below the calibrated threshold.
Common Causes
30%
Low or contaminated DEF fluid causing insufficient ammonia production
25%
Failed or clogged DEF injector preventing proper dosing
20%
Degraded or contaminated SCR catalyst substrate
15%
Faulty NOx sensors providing inaccurate readings
10%
DEF system air leaks or frozen DEF lines restricting flow
Diagnostic Steps
1
Step 1: Test DEF quality using refractometer - must read 32.5% concentration; check DEF level and expiration
2
Step 2: Monitor NOx sensor readings upstream and downstream of SCR catalyst during steady-state driving to calculate actual conversion efficiency
3
Step 3: Perform DEF injector flow test and inspect spray pattern using dealer-level scan tool commands
4
Step 4: Check for DEF system leaks, restrictions, or crystallization in lines and injector
5
Step 5: Verify proper exhaust temperature for SCR operation (minimum 400°F) and adequate DEF dosing rates
Estimated Repair Cost
$400 - $4,000
Parts + labor, varies by vehicle and location
The SCR NOx catalyst on Bank 1 is not reducing nitrogen oxide emissions to acceptable levels. The system detects that NOx conversion efficiency has fallen below the calibrated threshold.
The most common cause of P20EE (SCR NOx Catalyst Efficiency Below Threshold Bank 1) is: Low or contaminated DEF fluid causing insufficient ammonia production
Typical repair costs for P20EE range from $400 to $4,000, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but may experience reduced performance and enter limp mode after extended operation. Emissions compliance is compromised.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20EE to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Emissions Control System - SCR/DEF
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
