WOMS
P code powertrain Medium severity

P066A Cylinder 1 Glow Plug Control Circuit Low

The OBD2 code P066A indicates a low voltage or malfunction in the glow plug control circuit for cylinder 1, which can affect the engine's cold starting performance

Definition

The OBD2 code P066A indicates a low voltage or malfunction in the glow plug control circuit for cylinder 1, which can affect the engine's cold starting performance

Common causes

  • Faulty glow plug
  • Damaged wiring or connectors
  • Failed glow plug control module
  • Poor electrical connections
  • Short circuit in the glow plug circuit
  • Open circuit in the glow plug circuit
  • Faulty engine control module (ECM)

Common misdiagnoses

  • Faulty glow plug
  • Bad glow plug relay
  • Wiring issues or shorts in the circuit
  • Faulty engine control module (ECM)
  • Incorrectly diagnosed fuel system issues
  • Misdiagnosed injector problems
  • Battery or charging system issues
  • Faulty temperature sensor
  • Air intake issues
  • Exhaust 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 Glow Plug

    Visual Inspection: Check the glow plug for any signs of damage, corrosion, or wear. Ensure that the connections are secure and free of debris

  3. 3. Resistance Test

    Use a multimeter to measure the resistance of the glow plug. A typical glow plug should have a resistance value within the manufacturer's specifications (usually a few ohms). If the resistance is too high or infinite, the glow plug may be faulty

  4. 4. Check the Glow Plug Control Module

    Inspect the glow plug control module (if equipped) for any signs of damage or corrosion. Ensure that all connections are secure

  5. 5. Test the module according to the manufacturer's specifications to ensure it is functioning correctly

  6. 6. Inspect Wiring and Connectors

    Check the wiring harness and connectors leading to the glow plug and control module for any signs of damage, fraying, or corrosion

  7. 7. Look for any loose or broken connections that could cause a low voltage reading

  8. 8. Test Voltage Supply

    With the ignition on (but the engine off), use a multimeter to check the voltage at the glow plug connector. You should see battery voltage (typically around 12V). If the voltage is low or absent, there may be an issue with the power supply to the glow plug

  9. 9. Check Ground Connections

    Ensure that the ground connections for the glow plug and control module are clean and secure. A poor ground can lead to low voltage readings

  10. 10. Inspect Engine Control Module (ECM)

    If all other components check out, there may be an issue with the ECM. Check for any software updates or recalls related to the ECM that may address the issue

  11. 11. Clear Codes and Test Drive

    After performing the necessary repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  12. 12. Consult Repair Manual

    If the issue persists, consult the vehicle's repair manual for specific diagnostic procedures and specifications related to the glow plug system

  13. 13. Seek Professional Help

    If you are unable to diagnose or fix the issue, it may be best to consult a professional mechanic or technician who has experience with diesel engines and glow plug systems. By following these steps, you should be able to identify and resolve the issue related to the P066A code