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Technical Description of OBD-II Trouble Code
Bank 2 NOx Trap Efficiency Below Threshold
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all vehicles manufactured from 1996 onwards (Nissan, Honda, Infiniti, Ford, Dodge, Acura, Toyota, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
A stored P2001 code indicates that the powertrain control module (PCM) has detected a level of nitric oxide (NOx) higher than the programmed limit. Bank 2 refers to the side of the engine that does not contain the #1 cylinder.
NOx is produced as an exhaust emission by the internal combustion engine. Catalytic converter systems used to reduce NOx in gas burning engines are not as effective in diesel engines due to the higher oxygen content of spent exhaust gases in diesels. Therefore, diesel engines require a NOx trap or NOx adsorption system as a secondary method of NOx reduction. Diesel vehicles are equipped with selective catalytic reduction (SCR) systems, which include the NOx trap.
A web of zeolite compounds is used to trap the NOx molecules and prevent their release into the atmosphere. This web is secured inside a housing that resembles a catalytic converter. The exhaust passes through the web, and the NOx is trapped inside.
To refresh the zeolite structure, a combustible or flammable chemical is introduced through an electronically controlled injection system. Diesel fuel is the most practical chemical for this purpose.
In SCR systems, NOx sensors are used to monitor NOx particles, similar to how oxygen sensors are used in gasoline engines. However, NOx sensors do not affect fuel delivery adaptation strategy. The PCM monitors pre-catalyst and post-catalyst NOx sensor data to calculate NOx trap efficiency. This data is also used in the NOx reductant fluid delivery strategy.
Reductant injection is accomplished using an electronically controlled injector controlled by either the PCM or the SCR module. A remote reservoir contains NOx reductant fluid or diesel fuel, resembling a small fuel tank. Reductant pressure is generated using an electronically controlled fuel pump.
If the PCM detects a level of NOx higher than the programmed limit on bank 2, a P2001 code will be stored, and a malfunction indicator lamp may illuminate.
Symptoms
Symptoms of a P2001 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.
To diagnose a code P2001, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a vehicle information source like All Data (DIY).
Begin with a visual inspection of all system wiring harnesses and connectors, focusing on wiring near hot exhaust components and sharp exhaust shields, especially on bank 2.
Check the exhaust system for leaks and make necessary repairs.
Ensure that there is reductant in the SCR reservoir and that it is of suitable quality. Follow the manufacturer’s recommendations when adding reductant fluid.
Check exhaust gas recirculation (EGR) operation using the scanner. Repair any stored EGR codes before attempting to diagnose this code.
Connect the scanner to the vehicle diagnostic port to retrieve all stored trouble codes and freeze frame data. Write down this information as it may be helpful in diagnosing an intermittent code. Clear the codes from the system and start the engine. Allow the engine to reach normal operating temperature and test drive the vehicle to see if the code is reset.
If the code is reset, connect the scanner and observe NOx sensor data. Narrow the data stream to include only pertinent data for more accurate information.
If either of the NOx sensors are inactive, check for a blown fuse in the engine bay or under the dash. Most NOx sensors have a 4-wire design with a power wire, ground wire, and 2 signal wires. Use the DVOM and the service manual (or All Data) to test for battery voltage and ground signals. Test sensor output with the engine at normal operating temperature and idling.
Additional diagnostic notes:
Professional Service
While we always recommend seeking mechanical solutions for this issue, if that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you are interested in this option, please upload your ECU file to our portal.
