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P code powertrain Medium severity

P204C Reductant Pressure Sensor Circuit Low

The OBD2 code P204C indicates that the reductant pressure sensor circuit is reading a low voltage or signal, which may suggest a malfunction in the sensor or its wiring, affecting the vehicle's emissions control system

Definition

The OBD2 code P204C indicates that the reductant pressure sensor circuit is reading a low voltage or signal, which may suggest a malfunction in the sensor or its wiring, affecting the vehicle's emissions control system

Common causes

  • Faulty reductant pressure sensor
  • Wiring issues (shorts, opens, or corrosion)
  • Poor electrical connections
  • Low reductant fluid level
  • Defective reductant pump
  • Blocked or restricted reductant lines
  • Faulty engine control module (ECM)

Common misdiagnoses

  • Faulty reductant pressure sensor
  • Wiring issues or short circuits
  • Defective diesel exhaust fluid (DEF) pump
  • Low DEF level
  • Blocked or restricted DEF lines
  • Faulty engine control module (ECM)
  • Incorrect DEF quality or contamination
  • Exhaust system leaks

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 Pressure Sensor

    Locate the reductant pressure sensor and visually inspect it for any signs of damage, corrosion, or loose connections

  3. 3. Ensure that the sensor is properly connected and that the wiring harness is intact

  4. 4. Test the Reductant Pressure Sensor

    Use a multimeter to test the sensor's resistance and voltage output according to the manufacturer's specifications

  5. 5. Compare the readings to the expected values. If the readings are outside the specified range, the sensor may be faulty and need replacement

  6. 6. Check the Wiring and Connectors

    Inspect the wiring and connectors leading to the reductant pressure sensor for any signs of wear, fraying, or corrosion

  7. 7. Repair or replace any damaged wiring or connectors

  8. 8. Inspect the Reductant System

    Check the entire reductant system for leaks or blockages that could affect pressure readings

  9. 9. Ensure that the reductant (urea) is at the correct level and that the system is functioning properly

  10. 10. Test the Power Supply

    Verify that the sensor is receiving the correct voltage from the vehicle's power supply. Check the fuse related to the reductant system

  11. 11. If there is no power, trace the circuit back to find the source of the issue

  12. 12. Check for Ground Issues

    Ensure that the sensor has a good ground connection. A poor ground can lead to incorrect readings and trigger the code

  13. 13. Clear the Codes and Test Drive

    After performing the checks and repairs, clear the trouble codes using the OBD-II scanner

  14. 14. Take the vehicle for a test drive to see if the code reappears. Monitor the performance of the reductant system

  15. 15. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to the P204C code

  16. 16. Seek Professional Help

    If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who has experience with diesel emissions systems. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P204C code