WOMS
P code powertrain Medium severity

P20C3 Reductant Heater "C" Control Circuit Low

The OBD2 code P20C3 indicates a low voltage or malfunction in the control circuit for the reductant heater "C," which is part of the diesel exhaust fluid (DEF) system, affecting the heating element responsible for...

Definition

The OBD2 code P20C3 indicates a low voltage or malfunction in the control circuit for the reductant heater "C," which is part of the diesel exhaust fluid (DEF) system, affecting the heating element responsible for maintaining the proper temperature of the DEF

Common causes

  • Faulty reductant heater "C"
  • Open or shorted wiring in the control circuit
  • Poor electrical connections or corroded terminals
  • Failed power relay or fuse
  • Malfunctioning engine control module (ECM)
  • Faulty temperature sensor related to the reductant system

Common misdiagnoses

  • Faulty reductant heater
  • Wiring issues or shorts in the circuit
  • Defective engine control module (ECM)
  • Low coolant level
  • Faulty temperature sensor
  • Issues with the diesel exhaust fluid (DEF) system
  • Problems with the exhaust aftertreatment system
  • Incorrectly diagnosed fuel system issues

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 "C" and visually inspect it for any signs of damage, corrosion, or loose connections

  3. 3. Check the wiring harness and connectors for fraying, breaks, or poor connections

  4. 4. Test the Reductant Heater

    Use a multimeter to measure the resistance of the reductant heater. Compare the reading to the manufacturer's specifications. A reading outside the specified range may indicate a faulty heater

  5. 5. Check the Control Circuit

    Inspect the control circuit for continuity. Use a multimeter to check for any breaks in the wiring or poor connections that could cause a low signal

  6. 6. Check the voltage at the heater connector while the engine is running to ensure it is receiving the correct voltage

  7. 7. Inspect the Fuse

    Check the fuse associated with the reductant heater circuit. A blown fuse can cause the circuit to read low

  8. 8. Examine the Powertrain Control Module (PCM)

    If all other components check out, the issue may lie with the PCM. Ensure that the PCM is functioning correctly and that it is sending the proper signals to the reductant heater

  9. 9. Check for Software Updates

    Sometimes, manufacturers release software updates for the PCM that can resolve issues related to control circuits. Check with the manufacturer or a dealership for any available updates

  10. 10. Clear Codes and Test Drive

    After performing repairs or replacements, clear the trouble codes and take the vehicle for a test drive to see if the code returns

  11. 11. Consult Technical Service Bulletins (TSBs)

    Look for any TSBs related to the P20C3 code for your specific vehicle make and model. Manufacturers may have specific recommendations or known issues that can assist in troubleshooting

  12. 12. Seek Professional Help

    If the issue persists after performing the above 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 P20C3 code