WOMS
P code powertrain High severity

P20EE SCR NOx Catalyst Efficiency Below Threshold Bank 1

The OBD2 code P20EE indicates that the Selective Catalytic Reduction (SCR) system's NOx catalyst is not performing efficiently enough to reduce nitrogen oxides (NOx) emissions in Bank 1, falling below the required...

Definition

The OBD2 code P20EE indicates that the Selective Catalytic Reduction (SCR) system's NOx catalyst is not performing efficiently enough to reduce nitrogen oxides (NOx) emissions in Bank 1, falling below the required threshold

Common causes

  • Faulty NOx sensor
  • Defective SCR catalyst
  • Exhaust leaks
  • Incorrect DEF (Diesel Exhaust Fluid) quality or contamination
  • Low DEF level
  • Faulty or clogged injector for DEF
  • Wiring or connector issues in the NOx sensor circuit
  • Engine control module (ECM) software issues
  • Poor engine performance or misfires
  • High exhaust temperatures

Common misdiagnoses

  • Faulty NOx sensor
  • Defective SCR (Selective Catalytic Reduction) system
  • Clogged diesel particulate filter (DPF)
  • Exhaust leaks
  • Fuel quality issues
  • Incorrectly installed or damaged exhaust components
  • Software or calibration issues in the engine control module (ECM)

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. Codes related to the SCR system, NOx sensors, or other emissions components can provide additional context

  2. 2. Inspect the SCR System

    Visual Inspection: Check the SCR system components, including the SCR catalyst, for any visible damage, leaks, or blockages

  3. 3. Examine the Exhaust System

    Look for any exhaust leaks before the SCR system that could affect performance

  4. 4. Check the NOx Sensors

    Sensor Functionality: Test the NOx sensors (upstream and downstream of the SCR catalyst) for proper operation. Use a multimeter or scan tool to check the sensor readings against manufacturer specifications

  5. 5. Wiring and Connectors

    Inspect the wiring and connectors for damage, corrosion, or loose connections

  6. 6. Inspect the DEF System

    Diesel Exhaust Fluid (DEF): Ensure that the DEF tank is full and that the fluid is not contaminated. Low DEF levels or poor-quality DEF can affect SCR performance

  7. 7. DEF Injector

    Check the DEF injector for clogs or malfunctions. A faulty injector can lead to improper dosing of DEF into the exhaust stream

  8. 8. Check for Exhaust Restrictions

    Inspect the exhaust system for any restrictions, such as clogged diesel particulate filters (DPF) or other components that could impede exhaust flow

  9. 9. Perform a System Reset

    After addressing any issues, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  10. 10. Monitor Live Data

    Use a scan tool to monitor live data from the NOx sensors and SCR system while driving. Look for any abnormal readings that could indicate a problem

  11. 11. Check for Software Updates

    Verify if there are any software updates or recalls for the vehicle's engine control module (ECM) that may address known issues with the SCR system

  12. 12. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the specific make and model of the vehicle that may provide guidance on common issues and fixes for the P20EE code

  13. 13. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking assistance from a qualified technician or dealership with experience in diesel emissions systems.Conclusion Troubleshooting the P20EE code involves a systematic approach to inspect and test various components of the SCR system. Addressing any identified issues should help restore the efficiency of the NOx catalyst and clear the code