WOMS
P code powertrain High severity

P20C4 Reductant Heater "C" Control Circuit High

The OBD2 code P20C4 indicates that there is a high voltage detected in the control circuit for the reductant heater "C," which is part of the diesel exhaust fluid (DEF) system

Definition

The OBD2 code P20C4 indicates that there is a high voltage detected in the control circuit for the reductant heater "C," which is part of the diesel exhaust fluid (DEF) system

Common causes

  • Faulty reductant heater "C"
  • Short circuit in the control circuit
  • Open circuit in the control circuit
  • Damaged wiring or connectors
  • Faulty engine control module (ECM)
  • Corroded or poor electrical connections
  • Failed relay or fuse related to the reductant heater

Common misdiagnoses

  • Faulty reductant heater
  • Wiring issues or short circuits
  • Defective engine control module (ECM)
  • Faulty temperature sensor
  • Issues with the reductant pump
  • Incorrectly diagnosed fuel system problems
  • Misinterpretation of related codes
  • 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 Wiring and Connectors

    Visually inspect the wiring and connectors associated with the reductant heater "C". 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 "C" using a multimeter. Compare the resistance reading to the specifications provided in the vehicle's service manual

  5. 5. If the resistance is too high or infinite, the heater may be faulty and require replacement

  6. 6. Check the Control Circuit

    Inspect the control circuit for any issues. This includes checking the voltage at the connector when the vehicle is running. Ensure that the voltage is within the expected range

  7. 7. If the voltage is too high, there may be a short circuit somewhere in the wiring

  8. 8. Examine the Power Supply

    Ensure that the power supply to the reductant heater is functioning correctly. Check fuses and relays associated with the reductant heater circuit

  9. 9. Replace any blown fuses or faulty relays

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

    If all other components check out, the issue may lie with the ECM. Ensure that the ECM is functioning properly and is sending the correct signals to the reductant heater

  11. 11. In some cases, reprogramming or updating the ECM may be necessary

  12. 12. Clear Codes and Test Drive

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

  13. 13. Take the vehicle for a test drive to see if the code returns. Monitor the system to ensure it operates correctly

  14. 14. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the P20C4 code for your specific vehicle make and model. Manufacturers may have issued guidance or solutions for known issues

  15. 15. Seek Professional Help

    If you are unable to diagnose or resolve the issue, consider seeking help from a qualified mechanic or dealership. They will have the tools and expertise to perform more in-depth diagnostics. By following these steps, you should be able to identify and resolve the issue related to the P20C4 code. Always refer to the vehicle's service manual for specific procedures and specifications