P20EE: SCR NOx Catalyst Efficiency Below Threshold (Bank 1)

What does P20EE mean?

P20EE is a generic OBD-II code: SCR NOx Catalyst Efficiency Below Threshold, Bank 1. The ECU compares the NOx readings before and after the SCR catalyst and sets the code when the catalyst does not reduce NOx as much as expected.

It appears on diesel engines that use an AdBlue / DEF (urea) injection system.

Common causes

• Poor quality, old or contaminated AdBlue / DEF.
• A failing upstream or downstream NOx sensor.
• A degraded or contaminated SCR catalyst.
• A faulty dosing injector or pump, or a leak in the AdBlue system.
• Exhaust leaks close to the NOx sensors.

Typical symptoms

• Check engine light.
• An AdBlue or emissions warning on the dashboard.
• On some vehicles, reduced power or a restart countdown. This varies by model.

Diagnose first

Read live NOx sensor data, check the AdBlue quality and level, and inspect the dosing system. Replacing a failed part fixes the cause. DTC off only removes the code from the ECU file.

P20EE DTC off for Denso ECU files

If you work on competition or off-road vehicles and need P20EE disabled in a Denso ECU file, upload your readout and enter P20EE in the DTC list. You can add related codes you also want disabled, for example P2200 (NOx sensor circuit), in the same request.

See our Denso Gen 4 guide for what to send us, and the flashing checklist before you write the file.