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P20BF Reductant Heater "B" Control Circuit Low

The OBD2 code P20BF indicates a low voltage or malfunction in the control circuit for the reductant heater "B," which is part of the diesel exhaust fluid (DEF) system used to reduce emissions

Definition

The OBD2 code P20BF indicates a low voltage or malfunction in the control circuit for the reductant heater "B," which is part of the diesel exhaust fluid (DEF) system used to reduce emissions

Common causes

  • Faulty reductant heater "B"
  • Open or shorted wiring in the control circuit
  • Poor electrical connections or corroded terminals
  • Failed control module
  • Blown fuse related to the reductant heater circuit
  • Faulty temperature sensor
  • Issues with the power supply to the 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 dosing system
  • Problems with the exhaust aftertreatment system

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 "B" and visually inspect it for any signs of damage, corrosion, or loose connections

  3. 3. Check the wiring harness and connectors for fraying, breaks, or poor connections

  4. 4. Test the Reductant Heater

    Use a multimeter to measure the resistance of the reductant heater. Compare the reading to the manufacturer's specifications. A reading outside the specified range may indicate a faulty heater

  5. 5. Check the Control Circuit

    Inspect the control circuit for continuity. Use a multimeter to check for any breaks in the wiring or poor connections

  6. 6. Ensure that the ground connections are secure and free of corrosion

  7. 7. Inspect the Fuse

    Check the fuse associated with the reductant heater circuit. If the fuse is blown, replace it and see if the code returns

  8. 8. Examine the Power Supply

    Verify that the reductant heater is receiving the correct voltage. Use a multimeter to check the voltage at the heater connector while the vehicle is running

  9. 9. Check for Short Circuits

    Inspect the wiring for any signs of short circuits or grounding issues that could cause the control circuit to read low

  10. 10. Review the Engine Control Module (ECM)

    If all other components check out, the issue may lie within the ECM. Ensure that the software is up to date and consider reprogramming or replacing the ECM if necessary

  11. 11. Clear the Codes and Test Drive

    After performing the necessary repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns

  12. 12. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the P20BF code for your specific vehicle make and model. Manufacturers may have issued guidance or fixes for known issues.1

  13. 13. Seek Professional Help

    If the issue persists after following these steps, it may be best to consult a professional mechanic or technician who has experience with diesel engines and SCR systems. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P20BF code