Poor-quality, diluted or contaminated AdBlue (DEF); Faulty or clogged AdBlue dosing injector; Faulty upstream or downstream NOx sensor; Degraded or contaminated SCR catalyst; Exhaust leaks near the sensors.

SCR / AdBlue

P20EE SCR NOx Catalyst Efficiency Below Threshold (Bank 1)

Q: What does P20EE mean?

SCR NOx Catalyst Efficiency Below Threshold (Bank 1). The ECU compares the NOx levels measured by the upstream and downstream NOx sensors to calculate the conversion efficiency of the SCR catalyst. P20EE is set when the calculated efficiency stays below the calibrated threshold.

The ECU compares the NOx levels measured by the upstream and downstream NOx sensors to calculate the conversion efficiency of the SCR catalyst. P20EE is set when the calculated efficiency stays below the calibrated threshold.

Common causes

Poor-quality, diluted or contaminated AdBlue (DEF)
Faulty or clogged AdBlue dosing injector
Faulty upstream or downstream NOx sensor
Degraded or contaminated SCR catalyst
Exhaust leaks near the sensors

Typical symptoms

Check engine light and/or AdBlue or emissions warning on
Countdown to engine start restriction on many vehicles
Reduced power or limp mode
Urea crystal deposits around the dosing injector

P20EE and NuoVolta

If the SCR/AdBlue system has been removed or disabled for off-road or motorsport use, where permitted by law, the NuoVolta AdBlue / SCR / NOx Removal solution adjusts the ECU calibration and the DTC removal feature can disable this code. On a working system, check AdBlue quality, the dosing injector and the NOx sensors first.

AdBlue / SCR / NOx Removal Available for 121 ECUs

Related codes

P203FReductant (AdBlue/DEF) Level Too Low P2047Reductant (AdBlue/DEF) Injector Circuit/Open (Bank 1 Unit 1) P20E8Reductant (AdBlue/DEF) Pressure Too Low

Diagnose and repair real faults first. Removing or disabling emission systems is only permitted where allowed by law, for example for off-road or motorsport use.