P20EE P20EE00 SCR NOX Catalyst Efficiency below Threshold Error Code Explained

While the latest diesel engines have gain popularity and preference over gasoline engines, we can’t neglect the fact that the production and emission of harmful gases from these diesel fueled vehicles creates notorious impact on the environment. Reason being, governments in many countries have insisted on installing SCR ( Selective Catalyst Reduction) system in all diesel vehicles manufactured after January 2010 such as Audi, Buick, Chevrolet, Ford, GMC, Mercedes-Benz, Subaru, Toyota, Volkswagen etc to make them law compliant on EPA emission standards. This attempt was made to reduce emission of Nitrogen Oxide (NOX), particulate matter (PM) and other pollutants in atmosphere to nearly zero levels.

SCR injects a metered amount of Diesel exhaust fluid (DEF) into the exhaust gas stream, entering the diesel particulate filter (DPF) to reduce oxides of nitrogen emissions and use NOX sensors to control exhaust NOX levels. This introduction of DEF allows the catalyst element to perform efficiently and allowing fewer NOX emissions to release in the atmosphere.

What is the Code P220EE ERROR?

SCR is working efficiently if accurately defined DEF is being injected into the exhaust to maintain exhaust temperature within acceptable parameters and promote optimum NOX filtration but if Powertrain control module (PCM) detects that the catalyst efficiency is insufficient, a OBD code P20EE will be stored in PCM and you will be warned through a malfunction indicator displaying a warning message “Service Engine Soon" or an illuminating lamp.

P20EE SCR NOX Catalyst Efficiency below Threshold Error Code Explained

What does this error mean?

OBD code P20EE means SCR NOX Catalyst Efficiency below Threshold Bank 1 Issue.

In an event of increased emissions from the exhaust system, and out of bound performance of SCR injection system, performance of the vehicle is hampered with affected utilization of fuel delivery system and resultantly, vehicle starts producing and emitting increased pollutants.

What are the Symptoms?

Before diagnosis of  a problem, symptoms needs to be observed carefully so it is really necessary for you to first precisely identify what the symptoms pointing to. A few common symptoms which may cause OBD code P220EE to store in PCM could be:

  • Reduction in fuel efficiency
  • Excessive black smoke from vehicle exhaust
  • Diminished engine performance
  • Other SCR related codes

Possible Causes

SCR NOX Catalyst efficiency below threshold bank 1 might have been possible due to any of the following reasons:

  • Leakage in exhaust system
  • Contaminated fuel
  • Failed Diesel Particulate Filter (DPF)
  • Defective NOX Sensor
  • Inaccurate Diesel Exhaust Fluid
  • Failed Selective Catalyst Reduction (SCR) Catalyst
  • Nitrogen Oxide NOX Sensor’s malfunction
  • SCR system component’s fault

The most common diagnostic trouble codes DTC:

  • 17277 - SCR NOx Catalyst Bank 1
  • P20EE00 - Efficiency too Low
  • P20EE SCR NOX Catalyst Efficiency below Threshold

From our experience, the most common issue with P20EE error code is faulty Nitrogen Oxide Nox control unit sensors.

So, we always recommend our customers to check these sensors, some cars have two of them while others have one NOX sensor and other particulate matters (PM), so there are different combinations fitted on each different vehicle. 

Diagnostic test

If you want a perfect solution, it is imperative to diagnose that the symptoms are related to which particular fault code. In order to perform a diagnosis for P220EE code, check and retrieve all the codes present and pertinent freeze frame data and record this information before clearing all the codes. Clear all the codes from ECU and make a test drive of the vehicle. After the test drive if PCM doesn’t enter readiness mode or the code is reset and you suspect that the fault appearing again is related to P220EE code, then go to the mechanic and he should follow these steps to diagnose the real problem.

  • Perform a visual inspection looking for signs of exhaust leaks
  • Check for the damaged wiring of NOX probe or control unit of NOX sensor
  • Check exhaust gas temperature sensor by using a multimeter.

How can we resolve P220EE or P20EE00 fault code?

Since P20EE error code is complicated with several possible causes so are you wondering how can you resolve it quickly without incurring much time and money cost? The cheapest and easiest way to fix any of these P20EE fault code is to replace nitrogen oxide (NOX) sensor's NS11A probe with new; so, we recommend that first you need to check for faulty NOX sensors and consider replacing it before investigating other causes. Now that you’ve replaced the probe on NOX sensor, it should be the end of diagnostic issues. Restoring your vehicle in its ideal condition is possible with the replacement of NOX sensors probe but even after the installation of new sensors P220EE error is flashing up, then you don’t need to worry, you can take your vehicle to the mechanic for investigating more complex causes of the error which may include:

  • Diesel Exhaust Fluid Heater replacement
  • Diesel Particulate Filter replacement
  • Exhaust System replacement
  • Faulty Reductant Injection valve replacement
  • PCM repair and reprogramming

This is very rare that replacing NOX probe or whole sensor doesn’t fix P20EE DTC diagnostic trouble code, in most of all cases it is successful.

If you need any suggestion, help or spare parts to fix P20EE trouble code, get in touch with Xenons4U!

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When a P20EE is stored in a diesel powered, OBD-II equipped vehicle, it means that the powertrain control module has detected that catalyst efficiency is below threshold for a certain engine bank. This particular code applies to the downstream catalytic converter (or NOx trap) for engine bank one.