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P0678 Glow Plug Control Module Circuit Range/Performance Problem

The OBD2 code P0678 indicates a problem with the glow plug control module circuit, specifically related to its range or performance, which may affect the operation of the glow plugs in a diesel engine

Definition

The OBD2 code P0678 indicates a problem with the glow plug control module circuit, specifically related to its range or performance, which may affect the operation of the glow plugs in a diesel engine

Common causes

  • Faulty glow plug control module
  • Bad glow plugs
  • Wiring issues (shorts or open circuits)
  • Poor connections or corroded terminals
  • Faulty engine control module (ECM)
  • Voltage supply issues
  • Grounding problems
  • Faulty sensors (e.g., temperature sensor)

Common misdiagnoses

  • Faulty glow plugs
  • Bad glow plug relay
  • Wiring issues or shorts in the circuit
  • Faulty engine control module (ECM)
  • Incorrectly calibrated or faulty sensors (e.g., temperature sensors)
  • Battery or charging system problems
  • Fuel system issues (e.g., low fuel pressure)
  • Injector problems

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues

  2. 2. Inspect the Glow Plugs

    Visual Inspection: Check the glow plugs for physical damage, corrosion, or carbon buildup

  3. 3. Resistance Testing

    Use a multimeter to measure the resistance of each glow plug. Compare the readings to the manufacturer's specifications. A faulty glow plug may show an open circuit or significantly different resistance

  4. 4. Check the Glow Plug Control Module

    Visual Inspection: Inspect the glow plug control module for signs of damage, corrosion, or loose connections

  5. 5. Connector Check

    Ensure that all electrical connectors are secure and free of corrosion. Clean any corroded connections

  6. 6. Test the Glow Plug Control Circuit

    Voltage Testing: With the ignition on (but the engine off), use a multimeter to check for voltage at the glow plug control module and at each glow plug. Ensure that the voltage is within the specified range

  7. 7. Ground Testing

    Check the ground connections for the glow plug control module and ensure they are secure and free of corrosion

  8. 8. Inspect Wiring and Connectors

    Look for damaged, frayed, or shorted wiring in the glow plug circuit. Repair or replace any damaged wiring as necessary

  9. 9. Check for any loose or corroded connectors in the circuit

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

    If all other components check out, the issue may lie with the ECM. Ensure that the ECM is functioning properly and that it is receiving the correct signals from the glow plug control module

  11. 11. Perform a System Reset

    After addressing any issues found, 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 Technical Service Bulletins (TSBs)

    Check for any manufacturer-specific TSBs related to the P0678 code for your vehicle make and model. There may be known issues or recalls that could provide additional guidance

  13. 13. Seek Professional Help

    If the problem persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with diesel engines and glow plug systems. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P0678 code. Always refer to the vehicle's service manual for specific procedures and specifications