WOMS
P code powertrain Medium severity

P20BB Reductant Heater "A" Control Circuit Low

The OBD2 code P20BB indicates a low voltage or malfunction in the control circuit for the reductant heater "A," which is part of the diesel exhaust fluid (DEF) system, affecting the heating element that helps maintain...

Definition

The OBD2 code P20BB indicates a low voltage or malfunction in the control circuit for the reductant heater "A," which is part of the diesel exhaust fluid (DEF) system, affecting the heating element that helps maintain the proper temperature for the reductant

Common causes

  • Faulty reductant heater
  • Open or shorted wiring in the control circuit
  • Bad connector or corroded terminals
  • Failed power supply to the heater
  • Faulty engine control module (ECM)
  • Poor ground connection
  • Blown fuse related to the reductant heater circuit

Common misdiagnoses

  • Faulty reductant heater
  • Wiring issues or shorts in the circuit
  • Defective engine control module (ECM)
  • Low DEF (diesel exhaust fluid) level
  • Faulty temperature sensor
  • Issues with the DEF injector
  • Problems with the exhaust aftertreatment system
  • Incorrectly diagnosed fuel system issues

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if there are multiple issues

  2. 2. Inspect the Reductant Heater

    Locate the reductant heater and visually inspect it for any signs of damage, corrosion, or physical wear

  3. 3. Check the electrical connectors for any signs of damage, corrosion, or loose connections

  4. 4. Test the Reductant Heater

    Use a multimeter to measure the resistance of the reductant heater. Compare the reading to the specifications provided in the vehicle’s service manual

  5. 5. If the resistance is outside the specified range, the heater may be faulty and require replacement

  6. 6. Check the Wiring and Connectors

    Inspect the wiring harness and connectors leading to the reductant heater for any signs of damage, fraying, or short circuits

  7. 7. Ensure that all connections are secure and free of corrosion

  8. 8. Test the Control Circuit

    Check the voltage and ground at the reductant heater connector while the vehicle is running. Ensure that the control circuit is receiving the correct voltage as specified in the service manual

  9. 9. If there is no voltage or ground, trace the wiring back to the control module to identify any breaks or shorts

  10. 10. Inspect the Control Module

    If the wiring and heater are in good condition, the issue may lie with the engine control module (ECM) or the reductant control module

  11. 11. Check for any software updates or recalls related to the control module

  12. 12. Check for Fluid Leaks

    Inspect the area around the reductant heater for any signs of fluid leaks, which could indicate a problem with the SCR system

  13. 13. Clear Codes and Test Drive

    After performing repairs or replacements, clear the trouble codes using the OBD-II scanner

  14. 14. Take the vehicle for a test drive to see if the code returns

  15. 15. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the P20BB code for your specific vehicle make and model. Manufacturers may have specific fixes or recommendations

  16. 16. Seek Professional Help

    If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who specializes in diesel engines and emissions systems. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P20BB code. Always refer to the vehicle's service manual for specific procedures and specifications