P0679 - Cylinder No. Glow Plug DTC Circuit 9 (Glow Plug Circuit DTC for Cylinder No. 9)

Introduction

The DTC P0679 trouble code indicates a problem in the glow plug circuit for cylinder number 9 in a diesel engine. This code is part of a self-diagnostic system that monitors various engine components, helping to ensure optimal operation and reduce polluting emissions. Glow plugs are essential to the efficient starting and operation of a diesel engine, especially in cold conditions. In this article, we will explore the symptoms, causes, diagnosis, and possible solutions for the P0679 trouble code.

Symptoms

Symptoms associated with the DTC code P0679 can vary, but some of the more common ones include:

  • Difficulty starting the engine, especially at low temperatures
  • Slowdowns or irregularities during engine operation
  • Check Engine Light (MIL) on dashboard comes on
  • Increased emission of black smoke from the exhaust pipe
  • Increased fuel consumption

Cause

The causes of the DTC P0679 code can be many and range from electrical problems to mechanical failures. Here are some of the most common causes:

  • Faulty glow plug :
    One of the most common causes is a faulty or burned out glow plug. If cylinder 9 is not getting enough heat, the engine will have trouble starting.

  • Connection problems :
    Damaged or corroded wires or connectors can interrupt the glow plug circuit, preventing it from functioning properly.

  • Engine control unit (ECU) malfunction :
    The ECU may not be sending the correct signal to the glow plug, causing the error.

  • Faulty engine temperature sensor :
    If the temperature sensor is not working properly, it could cause the glow plugs to fire incorrectly.

  • Power problems :
    A discharged battery or a faulty alternator can affect the power supply to the glow plug circuit.

Diagnosis

Diagnosing the P0679 code requires a systematic approach. Here are the steps to follow:

  1. OBD-II Scanner :
    Use an OBD-II scanner to confirm the presence of DTC code P0679, and also check for other related codes such as P0678 (glow plugs cylinder 8) or P0677 (glow plugs cylinder 7) which may indicate a larger problem in the glow plug system.

  2. Visual inspection :
    Check the glow plug wiring and connectors for signs of wear, corrosion, or damage.

  3. Glow plug test :
    Use a multimeter to test the resistance of the glow plugs. A very high or infinite resistance indicates that the glow plug is defective.

  4. Power check :
    Measure the voltage at the glow plug terminals while the engine is running to ensure they are receiving the correct power.

  5. Control unit check :
    If all components appear to be working properly, it is advisable to perform an engine control unit check.

Resolution and repair

Once you have identified the problem, you can proceed with the resolution. Here are the recommended steps:

  • Replacing the spark plug :
    If the glow plug is defective, replace it. Make sure to use high quality replacement parts to ensure durability.

  • Wiring repair or replacement :
    If you find any damaged wiring, repair or replace it to restore circuit continuity.

  • Voltage control :
    If the voltage is incorrect, check the battery and alternator to make sure they are working properly. The battery or alternator may need to be replaced.

  • Replacing the temperature sensor :
    If the temperature sensor is faulty, replace it to ensure accurate readings.

  • DTC code reset :
    After making repairs, use the OBD-II scanner to clear the DTC code and monitor the vehicle to ensure the problem has been resolved.

Insight: Components involved in the failure

Glow plugs

Glow plugs are heating elements that are activated to preheat the combustion chamber before the engine starts. Each glow plug is connected to the engine control unit (ECU), which controls its operation based on engine temperature and environmental conditions.

Engine Control Unit (ECU)

The engine control unit is the main control unit that manages various engine systems, including the activation of the glow plugs. It receives information from sensors and sends activation signals to the glow plugs, thus influencing the starting process and the overall performance of the engine.

Conclusions

DTC P0679 is a major warning sign that there is a problem with the glow plug circuit for cylinder 9. Recognizing the symptoms and properly diagnosing the problem is essential to keeping your engine in tip-top condition and ensuring reliable starting. Through thorough inspection and proper troubleshooting, auto mechanics can effectively address this error code and improve vehicle performance. Don't forget to also consider other related DTC codes, as they may provide additional clues as to the cause of the malfunction.

Important
Not all OBD2 codes used by one manufacturer are used by other brands, and may not have the same meaning.
The information presented here is for informational purposes only. We are not responsible for any actions you take on your vehicle. If you have any concerns about repairing your vehicle, please contact your repair shop.