WOMS
P code powertrain Medium severity

P20C8 Reductant Heater "D" Control Circuit High

The OBD2 code P20C8 indicates that there is a high voltage detected in the control circuit for the reductant heater "D," which is part of the diesel exhaust fluid (DEF) system

Definition

The OBD2 code P20C8 indicates that there is a high voltage detected in the control circuit for the reductant heater "D," which is part of the diesel exhaust fluid (DEF) system

Common causes

  • Faulty reductant heater "D"
  • 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
  • Malfunctioning relay or fuse related to the reductant heater

Common misdiagnoses

  • Faulty reductant heater
  • Wiring issues or short circuits
  • Defective engine control module (ECM)
  • Incorrectly diagnosed fuel system issues
  • Problems with the exhaust aftertreatment system
  • Faulty sensors related to the reductant system
  • Issues with the diesel exhaust fluid (DEF) quality or level
  • Problems with the wiring harness or connectors

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

    Locate the reductant heater "D" and visually inspect it for any signs of damage, corrosion, or loose connections

  3. 3. Check the wiring harness and connectors for frayed wires, broken connectors, or signs of wear

  4. 4. Test the Reductant Heater

    Use a multimeter to measure the resistance of the reductant heater. Compare the reading to the specifications provided in the vehicle's service manual

  5. 5. If the resistance is outside the specified range, the heater may be faulty and require replacement

  6. 6. Check the Control Circuit

    Inspect the control circuit wiring for any shorts to ground or power. Look for damaged insulation or pinched wires

  7. 7. Test the voltage at the connector for the reductant heater while the engine is running. Ensure that the voltage is within the expected range

  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. If applicable, test the ground connections to ensure they are secure and free of corrosion

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

    If all other components check out, the issue may lie within the ECM. Check for software updates or reprogramming that may be necessary

  11. 11. In some cases, the ECM may need to be tested for proper operation

  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 P20C8 code for your specific vehicle make and model. Manufacturers may have issued guidance or solutions for known issues

  15. 15. Seek Professional Help

    If the problem 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 P20C8 code