Fault code P2001 – nitrogen oxides adsorber efficiency below threshold (Bank 2)

Fault code P2001 is called “Nitrogen oxides (NOx) Adsorber 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 P2001

Fault code P2001 means that the transmission control module (PCM) has detected nitrogen oxide (NOx) levels in excess of the programmed limit. Bank 2 refers to the side of the engine that does not contain cylinder number one.

Fault code P2001 – nitrogen oxides adsorber efficiency below threshold (Bank 2)

A diesel combustion engine emits nitrogen oxide (NOx) which is released in the exhaust gases. In order to reduce NOx emissions in diesel engines, a NOx trap or NOx adsorption system must be used.

Also, vehicles equipped with diesel engines use selective catalytic reduction (SCR) systems, of which the NOx trap is a part.

SCRs use NOx sensors in the same way as the oxygen sensors in gasoline engines, but they do not affect the fuel adaptation strategy. They monitor NOx particles instead of oxygen levels.

The PCM monitors NOx sensor data before and after the catalyst to calculate NOx capture efficiency. If the PCM detects NOx levels exceeding the programmed limit, code P2001 will be stored and the malfunction indicator light may illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P2001 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine control lamp on the control panel will light up (the code will be recorded in the memory as a malfunction).
  2. Excessive smoke from the car exhaust system.
  3. Possible loss of engine power.
  4. Excessive engine temperature.
  5. Increased fuel consumption.
  6. Unstable gear shifting patterns due to reduced engine speed.

When error P2001 appears, there are usually no serious problems with the vehicle’s drivability. However, if it is present, the vehicle is likely to fail the emission test.

Factors that can cause this error code

The error code P2001 can mean that one or more of the following problems have occurred:

  • Faulty or clogged NOx trap or trap element.
  • The reconditioning fluid injection system is defective.
  • Incorrect reducing fluid.
  • Faulty exhaust gas recirculation system.
  • Severe exhaust gas leakage in front of NOx adsorber.
  • Short-circuited or broken electrical wiring.
  • Poor electrical connection in the control circuit.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P2001

Some suggested steps for troubleshooting and fix the error code P2001:

  1. Connect the OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
  2. Clear the error codes from the computer memory.
  3. Test-drive the vehicle to see if the error appears again.
  4. If the code appears again, visually inspect the electrical wires, connectors.
  5. Inspect the reconstituting fluid injection system.
  6. Check the presence of the regenerating fluid and its compliance.
  7. Check the system for exhaust leaks, and NOx adsorber clogging.
  8. Test and replace the control module (PCM) if necessary.

Diagnose and repair of problems

It is best to start troubleshooting error P2001 by visually inspecting all wiring harnesses and system connectors. Inspect the wiring near the hot components and the sharp guard of the exhaust system.

Next, check the exhaust system for leaks and make repairs if necessary. Make sure the SCR reservoir has recovering fluid in it and that it meets the requirements.

Check NOx sensors

If any of the NOx sensors are inactive, check for a blown fuse in the engine compartment or under the instrument panel. Most NOx sensors are 4-wire with power, ground, and 2-signal wires.

Use a multimeter and service manual to check the voltage from the battery as well as the ground. Check the sensor output from the PCM at normal operating temperature as well as at idle.

If no problems are found, drive the vehicle at highway speeds for approximately 30 minutes. To raise the exhaust temperature enough to regenerate the adsorber.

On which vehicles does this problem occur most frequently

Fault code P2001 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Acura
  • Dodge
  • Ford
  • Honda
  • Infiniti
  • Mercedes-Benz (S220, W163, W203, W211, W220)
  • Nissan
  • Toyota
  • Volvo

Fault code P2001 can sometimes be found with other errors. The most common are the following: P2000, P2002, P2003.

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