WOMS
P code powertrain Medium severity

P20C5 Reductant Heater "D" Control Circuit/Open

The OBD2 code P20C5 indicates a malfunction in the control circuit for the reductant heater "D," which is responsible for heating the diesel exhaust fluid (DEF) to ensure proper operation.

Definition

The OBD2 code P20C5 indicates a malfunction in the control circuit for the reductant heater "D," 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

Common causes

  • Faulty reductant heater "D"
  • Open or shorted wiring in the control circuit
  • Bad connector or corroded terminals
  • Failed power supply to the heater
  • Malfunctioning engine control module (ECM)
  • Blown fuse related to the reductant heater circuit
  • Poor ground connection in the circuit

Common misdiagnoses

  • Faulty reductant heater
  • Open or shorted wiring in the circuit
  • Defective engine control module (ECM)
  • Issues with the reductant pump
  • Faulty temperature sensor
  • Problems with the exhaust aftertreatment system
  • Incorrectly diagnosed fuel system issues
  • Battery or charging system problems

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 "D". Look for signs of damage, corrosion, or loose connections

  3. 3. Pay special attention to any frayed wires or broken connectors that could cause an open circuit

  4. 4. Test the Reductant Heater

    If accessible, test the resistance of the reductant heater "D" using a multimeter. Compare the readings 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

    Inspect the control circuit for continuity. Use a multimeter to check for continuity between the control module and the reductant heater

  7. 7. If there is no continuity, trace the wiring back to find the break or fault

  8. 8. Examine the Power Supply

    Ensure that the reductant heater is receiving the proper voltage. Check the power supply to the heater while the vehicle is running

  9. 9. If there is no power, check the fuses and relays associated with the reductant heater circuit

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

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

  11. 11. Reprogramming or replacing the ECM may be necessary if it is determined to be faulty

  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 P20C5 code for your specific vehicle make and model. Manufacturers may have issued updates or fixes for known issues

  15. 15. 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 P20C5 code