WOMS
P code powertrain Medium severity

P20BD Reductant Heater "B" Control Circuit/Open

The OBD2 code P20BD indicates a malfunction in the control circuit for the reductant heater "B," which is responsible for heating the diesel exhaust fluid (DEF) to ensure proper operation.

Definition

The OBD2 code P20BD indicates a malfunction in the control circuit for the reductant heater "B," which is responsible for heating the diesel exhaust fluid (DEF) to ensure proper operation. The "Open" part of the code suggests a break or fault in the electrical circuit, preventing the heater from functioning correctly

Common causes

  • Faulty reductant heater "B"
  • Open circuit in the wiring harness
  • Damaged connectors or terminals
  • Short circuit in the wiring
  • Failed power supply to the heater
  • Faulty engine control module (ECM)
  • Corrosion or poor ground connection

Common misdiagnoses

  • Faulty reductant heater
  • Open or shorted wiring in the circuit
  • Defective engine control module (ECM)
  • Faulty temperature sensor
  • Issues with the diesel exhaust fluid (DEF) system
  • Problems with the reductant pump
  • Incorrectly installed or damaged connectors
  • Software issues in the ECM

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 Wiring and Connectors

    Visually inspect the wiring harness and connectors associated with the reductant heater "B." Look for signs of damage, corrosion, fraying, or loose connections

  3. 3. Ensure that all connectors are securely plugged in and that there are no bent pins

  4. 4. Test the Reductant Heater

    If accessible, test the resistance of the reductant heater using a multimeter. Compare the resistance reading to the specifications provided in the vehicle's service manual

  5. 5. If the resistance is out of range, the heater may be faulty and require replacement

  6. 6. Check the Control Circuit

    Use a multimeter to check for voltage and ground at the reductant heater connector while the vehicle is running. Ensure that the control circuit is receiving the proper voltage from the engine control module (ECM)

  7. 7. If there is no voltage, trace the wiring back to the ECM to identify any breaks or shorts in the circuit

  8. 8. Inspect the ECM

    If the wiring and heater are functioning correctly, the issue may lie within the ECM. Check for any software updates or recalls related to the ECM

  9. 9. In some cases, reprogramming or replacing the ECM may be necessary

  10. 10. Check for Short Circuits

    Inspect the wiring for any signs of short circuits to ground or to other circuits. This can cause the control circuit to open and trigger the P20BD code

  11. 11. Clear the Code and Test Drive

    After performing any repairs or replacements, clear the trouble codes using the OBD-II scanner 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 P20BD code for your specific vehicle make and model. Manufacturers may have issued guidance or solutions for known issues

  13. 13. Seek Professional Help

    If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with diesel exhaust systems and OBD-II diagnostics. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P20BD code. Always refer to the vehicle's service manual for specific procedures and specifications