WOMS
P code powertrain Medium severity

P20C0 Reductant Heater "B" Control Circuit High

The OBD2 code P20C0 indicates that there is a high voltage detected 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 P20C0 indicates that there is a high voltage detected 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"
  • Short circuit in the wiring or connectors
  • Open circuit in the wiring or connectors
  • Failed control module
  • Corroded or damaged connectors
  • Poor ground connection
  • Faulty relay or fuse related to the reductant 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., P20C1, P20C2)
  • Problems with the DEF (diesel exhaust fluid) quality or level
  • Issues with the exhaust aftertreatment system
  • Faulty sensors related to the reductant 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 Wiring and Connectors

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

  3. 3. Pay special attention to any frayed wires or broken connectors that could cause a short circuit or high resistance

  4. 4. Test the Reductant Heater

    If accessible, test the resistance of the reductant heater "B" using a multimeter. Compare the reading to the manufacturer's specifications. A reading that is too high or infinite indicates a faulty heater

  5. 5. If the heater is shorted, it may need to be replaced

  6. 6. Check the Control Circuit

    Inspect the control circuit for the reductant heater. This includes checking the voltage supply to the heater and ensuring that the control module is sending the correct signals

  7. 7. Use a multimeter to measure the voltage at the heater connector while the engine is running. It should match the specifications provided by the manufacturer

  8. 8. Examine the Engine Control Module (ECM)

    If the wiring and heater are in good condition, the issue may lie with the ECM. Check for any software updates or reprogramming that may be required

  9. 9. In some cases, the ECM may need to be tested or replaced if it is not sending the correct signals to the heater

  10. 10. Check for Ground Issues

    Ensure that the ground connections for the reductant heater circuit are secure and free of corrosion. A poor ground can lead to high resistance and trigger the code

  11. 11. Clear the Code and Test Drive

    After performing any repairs or replacements, clear the trouble code 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 P20C0 code for your specific vehicle make and model. Manufacturers may have issued guidance or fixes for known issues

  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 P20C0 code