What does code P20EE mean?
SCR NOx catalyst efficiency below threshold — Bank 1. The ECU determines that the Selective Catalytic Reduction (SCR) system is not reducing NOx emissions sufficiently. Very common in Euro 5+ and Euro 6 diesel vehicles with AdBlue system.
Symptoms seen in the workshop
- MIL on
- No-start countdown message
- Limp mode / limited power
- Start prevention (advanced countdown)
- Excessive AdBlue consumption
- Black smoke
Common causes of code P20EE
- Poor quality or contaminated AdBlue/DEF
- Blocked or crystallized AdBlue injector
- Faulty upstream or downstream NOx sensor
- AdBlue pump with insufficient pressure
- Degraded or contaminated SCR catalyst
- Exhaust leaks before SCR
- Outdated ECU software
Fix by ECU remapping
Complete ECU remapping solution:
1. AdBlue/SCR OFF (calibration): Deactivation of the complete AdBlue injection system, SCR monitoring, NOx sensors and no-start countdown.
2. DTC OFF: Deactivation of P20EE and all associated DTCs.
It is essential to also deactivate the no-start countdown logic that can prevent vehicle starting.
⚠️ Important: Disabling the DTC without the correct calibration of the related system (AdBlue OFF + SCR OFF + DTC OFF) is not a valid fix. Both the calibration maps and the diagnostic mask have to be modified.
Frequently asked questions about P20EE
What does P20EE mean?
It indicates SCR catalyst NOx reduction efficiency is below threshold. It is the primary AdBlue system DTC.
Can P20EE prevent engine start?
Yes. Many Euro 6 vehicles start a countdown that, if unresolved, prevents engine starting. ECU remapping eliminates this restriction.
