Fault code P20F2 – selective catalyst reduction NOx catalyst efficiency below threshold (Bank 2)

Fault code P20F2 is called “Selective Catalyst Reduction (SCR) NOx Catalyst Efficiency Below Threshold (Bank 2)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P20F2

Code P20F2 in a diesel engine vehicle means that the transmission control module has detected a Selective Catalyst Regeneration (SCR) efficiency below the threshold value. This error applies to the lower temperature sensor, Bank 2. Bank 2, is the engine cylinder group where cylinder number 1 is not located.

Although modern clean-burning diesel engines have many advantages over gasoline engines. But they tend to produce more of certain harmful exhaust gases. The most noticeable of these aggressive pollutants are nitrogen oxide ions (NOx).

Exhaust gas recirculation (EGR) systems help significantly reduce NOx emissions. But many of today’s high-powered diesel engines cannot meet today’s strict emissions standards with EGR alone. For this reason, selective catalyst reduction (SCR) systems have been developed.

SCR systems inject Diesel Exhaust Fluid (DEF) upstream of a catalytic converter or NOx catcher. The injection of DEF increases the temperature of the exhaust gases and allows the catalytic converter element to operate more efficiently. This increases the life of the catalyst and reduces NOx emissions.

Temperature sensors are placed before and after the catalyst to monitor its temperature and efficiency. The entire SCS system is controlled either by the PCM or by a stand-alone controller that communicates with the PCM.

The controller processes data from the temperature sensors as well as other parameters to determine the appropriate timing for DEF injection. Accurate DEF injection is necessary to keep the exhaust temperature within acceptable parameters and to ensure optimal NOx filtration.

If the PCM detects that the catalyst efficiency is insufficient for the minimum allowable parameters. Then code P20F2 will be stored and the malfunction indicator light may illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P20F2 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

1. The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
2. Other related fault codes may also be present.
3. Increased emission of harmful substances in the exhaust gases.
4. Increased fuel consumption.
5. Reduced engine power output.
6. Excessive black smoke from the vehicle’s tailpipe.
7. Sometimes symptoms may be absent despite a stored fault code.

Any stored codes related to the SCR Selective Catalyst Recovery System may initiate a shutdown of this system. Stored code P20F2 should be considered serious and corrected as soon as possible. If the code is not corrected, it may cause damage to the catalytic converter.

Factors that can cause this error code

The error code P20F2 can mean that one or more of the following problems have occurred:

• Damaged or faulty exhaust temperature sensor.
• Damaged or incorrectly wired exhaust gas temperature sensor.
• Defective Selective Catalytic Reduction (SCR) system.
• Defective SCR injector.
• Exhaust leaks in front of the catalytic converter.
• Installation of non-original or high-performance exhaust system components.
• Improper or insufficient DEF fluid.
• Sometimes the cause is a faulty SCR controller or programming error.

How to fix or reset OBD-2 code P20F2

Some suggested steps for troubleshooting and fix the error code P20F2:

1. Read all error codes stored in the vehicle’s PCM memory with an OBD-II scan tool.
2. Check the operation of the exhaust temperature oxygen sensor.
3. Diagnose any other error codes that may have caused code P20F2.
4. Repair any emission leaks.
5. Check the DEF fluid.
6. Test drive the vehicle to check the exhaust temperature sensor.
7. Replace or reprogram faulty SCR if necessary.

Diagnose and repair of problems

If there are no additional errors, clear fault code P20F2 and perform a short test drive. To allow the PCM to go into closed loop mode, then scan the system again and see if the code comes back.

Check the catalytic converter and leaks

Check for exhaust leaks, repair them if necessary. Inspect any electrical connections that are connected to the exhaust temperature sensor. Sometimes heat and vibration can cause the electrical connector to disconnect and the engine error indicator light will come on.

If a code is found, check the sensor operation to make sure it is working properly. Compare the displayed output signals with the values indicated in the manual.

Test temperature sensor, inspect wiring

Check the wiring harness that goes to the exhaust temperature sensor. It is important to make sure that there are no burned out, broken or severely loose spots. Which could hit any moving component while the car is in motion.

Check the operation of the sensor by thoroughly warming up the engine. Remember that the sensor will only work once it has reached its operating temperature.

Connect the sensor output to a multimeter and start the engine at about 2000-2500 rpm. The output should have a voltage fluctuating between 0.1 and 0.9 V. If the sensor output does not change or the response time is too long. This means you have a bad sensor, you should replace it.

Replacing the sensor will most likely correct the error. But sometimes, you need to replace the catalytic converter to fix the problem. If code P20F2 is combined with other codes, try fixing the other codes first.

On which vehicles does this problem occur most frequently

Fault code P20F2 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

• Audi
• Buick
• Chevrolet
• Ford
• GMC
• Mercedes-Benz
• Subaru
• Toyota
• Volkswagen

Fault code P20F2 can sometimes be found with other errors. The most common are the following: P20EC, P20ED, P20EE, P20EF, P20F0, P20F1, P20F3.

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