WOMS
P code powertrain High severity

P20BC Reductant Heater "A" Control Circuit High

The OBD2 code P20BC indicates that there is a high voltage signal detected in the reductant heater "A" control circuit, which is part of the diesel exhaust fluid (DEF) system used for emissions control

Definition

The OBD2 code P20BC indicates that there is a high voltage signal detected in the reductant heater "A" control circuit, which is part of the diesel exhaust fluid (DEF) system used for emissions control

Common causes

  • Faulty reductant heater
  • Short circuit in the wiring
  • Open circuit in the wiring
  • Faulty control module
  • Corroded or damaged connectors
  • Poor ground connection
  • Incorrect voltage supply to the heater

Common misdiagnoses

  • Faulty reductant heater
  • Wiring issues or shorts in the circuit
  • Defective engine control module (ECM)
  • Incorrectly diagnosed fuel system issues
  • Misinterpretation of related codes (e.g., P20B9, P20B8)
  • Problems with the DEF (diesel exhaust fluid) quality or level
  • Issues with the NOx sensor
  • Faulty connectors or terminals in the circuit

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

    Visually inspect the reductant heater for any signs of damage, corrosion, or loose connections. Ensure that the wiring harness and connectors are secure and free from damage

  3. 3. Test the Reductant Heater Circuit

    Use a multimeter to check the resistance of the reductant heater. Compare the readings to the manufacturer's specifications. A reading that is too high or too low may indicate a faulty heater

  4. 4. Check the Power Supply

    Verify that the reductant heater is receiving the correct voltage. Check the power and ground circuits to ensure they are functioning properly. Look for blown fuses or damaged wiring

  5. 5. Inspect the Control Module

    The Engine Control Module (ECM) or Powertrain Control Module (PCM) may be sending incorrect signals. Check for software updates or reprogramming needs. If necessary, perform a reset of the ECM/PCM

  6. 6. Examine the Wiring and Connectors

    Inspect the wiring harness for any signs of wear, fraying, or short circuits. Pay special attention to connectors for corrosion or poor contact

  7. 7. Check for Environmental Factors

    Ensure that the reductant heater is not exposed to excessive moisture or contaminants that could affect its operation

  8. 8. Perform a Functional Test

    If possible, perform a functional test of the reductant heater while monitoring the vehicle's data stream. This can help determine if the heater is operating as intended

  9. 9. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the P20BC code for your specific vehicle make and model. Manufacturers may have known issues or recommended fixes

  10. 10. Replace Faulty Components

    If any components are found to be faulty during testing (e.g., the reductant heater, wiring, connectors), replace them as necessary.1

  11. 11. Clear Codes and Test Drive

    After repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns. Monitor the system to ensure proper operation.1

  12. 12. 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 emissions systems. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P20BC code