Technical Description of OBD-II Trouble Code
The efficiency of the SCR NOx Catalyst is below the required threshold for Bank 1.
What does that mean?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer), including Audi, Buick, Chevrolet, Ford, GMC, Mercedes-Benz, Subaru, Toyota, Volkswagen, and others. However, the exact repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
When a P20EE code is stored in a diesel-powered, OBD-II equipped vehicle, it indicates that the powertrain control module has detected that the catalyst efficiency for a certain engine bank is below the required threshold. This code specifically applies to the downstream catalytic converter (or NOx trap) for engine bank one, which is the bank of the engine that contains the number one cylinder.
While modern, clean-burning diesel engines have several advantages over gasoline engines, they also tend to produce higher levels of certain harmful exhaust gases, particularly nitrogen oxide (NOx) ions.
To significantly reduce NOx emissions, exhaust gas recirculation (EGR) systems are used. However, many powerful diesel engines cannot meet strict federal emission standards using the EGR system alone. This is why selective catalytic reduction (SCR) systems were developed.
SCR systems inject diesel exhaust fluid (DEF) into the exhaust in front of the catalytic converter or NOx trap. The introduction of DEF raises the exhaust gas temperature, allowing the catalyst element to perform more efficiently. This extends the lifespan of the catalyst and reduces the release of NOx emissions into the atmosphere.
Oxygen (O2) sensors, NOx sensors, and temperature sensors are placed before and after the catalyst to monitor its temperature and efficiency. The entire SCR system is controlled by either the powertrain control module (PCM) or a stand-alone controller that interacts with the PCM. The controller monitors the O2, NOx, and temperature sensors, along with other inputs, to determine the appropriate time for DEF injection. Precise DEF injection is crucial to maintain exhaust temperature within acceptable parameters and ensure optimal NOx filtration.
If the PCM detects that the catalyst efficiency is below the minimum allowable parameters, it will store a P20EE code and may illuminate the malfunction indicator lamp.
What is the severity of this DTC?
Any stored SCR-related codes can result in the SCR system being disabled. The stored P20EE code should be considered severe and addressed as soon as possible to prevent catalyst damage.
What are some of the symptoms of the code?
Symptoms of a P20EE trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P20EE troubleshooting steps?
If there are any other stored SCR or exhaust emissions codes, or exhaust temperature codes, they should be addressed before attempting to diagnose the stored P20EE code.
Any pre-catalyst exhaust leaks should be repaired before attempting a diagnosis for this type of code.
To diagnose a P20EE code, you will need access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), an infrared thermometer with a laser pointer, and vehicle-specific SCR system diagnostic information.
Locating a technical service bulletin (TSB) that matches the vehicle’s year, make, and model, as well as the engine size, stored codes, and exhibited symptoms, could provide helpful diagnostic information.
Begin the diagnosis by visually inspecting the SCR injection system, exhaust temperature sensors, NOx sensors, and oxygen (O2) sensor harnesses and connectors. Repair or replace any burnt or damaged wiring and connectors before proceeding.
Next, locate the vehicle diagnostic connector and connect the scanner. Retrieve all stored codes and relevant freeze frame data, and record this information before clearing the codes. Then, test drive the vehicle until the PCM either enters readiness mode or the code is reset.
If the PCM enters readiness mode, the code is intermittent and may be more difficult to diagnose at this time. The conditions that contributed to the code being stored may need to worsen before a diagnosis can be made.
If the code is immediately reset, consult your source of vehicle information to obtain diagnostic flow charts, connector pinout charts, connector face views, component testing procedures, and specifications. This information will be necessary to complete the next steps of the diagnosis.
Observe the scanner data stream to compare exhaust (pre and post) O2, NOx, and temperature sensor data between engine banks. If inconsistencies are detected, test the respective sensors using the DVOM. Sensors that fail to comply with manufacturer specifications should be considered defective.
If all sensors and circuitry appear to be functioning as intended, suspect that the catalyst element is faulty or that the SCR system has failed.
