Fault-Code Library · AdBlue / SCR
P20EE: SCR NOx catalyst efficiency below threshold
The SCR system is not reducing NOx emissions as effectively as the ECU expects.
Common symptoms
- •AdBlue warning
- •Engine light
- •Possible restart countdown
- •No obvious drivability symptom
Likely causes
- •Biased NOx sensor
- •Incorrect AdBlue dosing
- •Poor fluid quality
- •Exhaust leak or aged SCR catalyst
First checks
- •Read upstream and downstream NOx values
- •Verify dosing and fluid quality
- •Check temperature data and related faults
Important
Parts substitution is expensive; diagnose the complete SCR system before replacement.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.