Code Definition

P20EE — NOx Catalyst Efficiency Below Threshold

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P20EE

P20EE is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P20EE is stored, the module has detected a signal or supply voltage lower than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P20EE is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The Engine Control Module (ECM) evaluates the efficiency of the Selective Catalytic Reduction (SCR) NOx catalyst by comparing signals from the upstream and downstream NOx sensors during defined steady state operating conditions. The SCR system injects urea solution (AdBlue or DEF) into the exhaust upstream of the catalyst, where it converts to ammonia and reduces oxides of nitrogen (NOx) into harmless nitrogen and water. DTC P20EE is set when the ECM determines that the NOx conversion efficiency of the SCR catalyst is below the calibrated minimum threshold over a defined drive cycle, meaning t...

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