P20EE is a generic OBD-II code: SCR NOx catalyst efficiency below threshold (bank 1). The engine control unit compares NOx levels before and after the SCR catalyst and finds that NOx is not being reduced enough.
Typical symptoms
- Check engine light and/or AdBlue/SCR warning
- Reduced power (limp mode) on some vehicles
- Start-restriction countdown on some vehicles
Possible causes
- Faulty upstream or downstream NOx sensor
- Faulty AdBlue injector / dosing module
- Poor quality or contaminated AdBlue
- Incorrect dosing or pressure
- Exhaust leak before the SCR catalyst
- Catalyst temperature out of range, or a catalyst that has lost efficiency
- Software issue on specific vehicles
Documented case: Peugeot Boxer III
HELLA documents Peugeot Boxer III 2.0 and 2.2 HDi (Euro 6.2) vehicles built between 01/09/2019 and 11/05/2021 showing “Engine start in 100 km no longer possible” with P20EE. The documented fix for these vehicles is a software update via the manufacturer portal.
This update applies only to the vehicles listed by HELLA. A software update is not a universal solution for P20EE; on other vehicles the cause is usually in the SCR hardware and must be diagnosed first.
What a technician should check
- Diagnose any NOx sensor codes first.
- Check AdBlue quality and concentration.
- Check injector/dosing operation and quantity with the correct test procedure.
- Check for exhaust leaks upstream of the SCR catalyst.
- Check NOx sensor values and catalyst temperature in live data.
- Check for manufacturer software updates for the vehicle.
When software work is justified
Only after the SCR system has been diagnosed, or when a manufacturer bulletin matches the vehicle. We do not disable or remove emissions systems on road vehicles.
When software will not fix it
If a sensor, the injector, AdBlue quality or the catalyst is at fault, a software change will not restore efficiency.
FAQ
Can I keep driving with the countdown?
When the countdown ends the engine may not restart. Get it diagnosed before the limit is reached.
Will new AdBlue fix P20EE?
Only if poor AdBlue was the cause. The other components still need checking.
Related T-Tronic services
Get help from T-Tronic
Send us the vehicle details, the full fault code list with sub-codes and the symptoms through our quote request form. We will tell you what should be checked first and whether a module repair makes sense.
Fault codes and their meanings can differ between model years and software versions. This guide is general information for diagnosis and does not replace manufacturer repair data.