P0679 DTC Code


In the world of automotive diagnostics, DTC (Diagnostic Trouble Code) is a crucial term. It helps identify potential issues within a vehicle’s systems and allows technicians to pinpoint the exact problem for effective repairs. One such DTC code is P0679, which relates to the Glow Plug Module Control Circuit High.

In this comprehensive guide, we will delve into the P0679 DTC code, its meaning, possible causes, symptoms, and diagnostics. Additionally, we will shed light on effective solutions to rectify this issue and ensure your vehicle’s optimal performance.

Understanding the P0679 DTC Code:

The P0679 DTC code specifically points towards a malfunction or fault within the Glow Plug Module Control Circuit High. Glow plugs are essential components in diesel engines, which assist in the combustion process by heating up the air in the combustion chamber. The purpose of the glow plug control module is to manage and regulate the glow plug operation.

When the control module detects a high voltage circuit reading or a fluctuation outside the specified range, it triggers the P0679 DTC code. This DTC code indicates that there is an issue within the glow plug module control circuit, impeding the smooth and effective operation of the glow plugs.

Potential Causes of P0679 DTC Code:

  1. Glow Plug Control Module Malfunction: The most common cause of the P0679 DTC code is a faulty glow plug control module. Over time, these modules can develop electronic or mechanical problems, leading to erratic voltage readings and ultimately triggering the code.

  2. Wiring Issues or Loose Connections: Another possible cause of the P0679 DTC code is wiring problems or loose connections within the glow plug control circuit. Damaged, frayed, or corroded wires can disrupt the electrical flow, resulting in high voltage readings.

  3. Glow Plug Malfunction: Faulty glow plugs can also contribute to the P0679 DTC code. If a glow plug becomes deteriorated or fails to function properly, it can cause abnormal voltage readings, triggering the code.

  4. ECM (Engine Control Module) Issues: In rare cases, problems within the ECM can lead to the P0679 DTC code. The ECM controls various aspects of an engine’s operation, including the glow plug control module. If the ECM malfunctions or fails, it can affect the voltage regulation within the glow plug circuit.

Common Symptoms of P0679 DTC Code:

Detecting the P0679 DTC code early on is crucial for prompt repairs and preventing further damage. Here are some common symptoms that may indicate the presence of this code:

  1. Malfunction Indicator Lamp (MIL) Illumination: When the P0679 DTC code triggers, the check engine light or MIL will illuminate on the vehicle’s dashboard. This serves as an initial warning sign and should not be ignored.

  2. Difficult Engine Start: If you experience difficulties starting your diesel engine, especially during colder temperatures, it may indicate glow plug issues related to the P0679 code. Faulty glow plugs can hinder the combustion process and make engine ignition a challenging task.

  3. Rough Engine Operation: Another symptom associated with the P0679 DTC code is rough engine operation. You may notice shaky or uneven idling, decreased engine performance, and potential misfires. These issues can lead to reduced fuel efficiency and overall vehicle drivability.

Diagnosing and Resolving the P0679 DTC Code:

Proper diagnosis is crucial to accurately resolve the P0679 DTC code. Here are the steps involved in diagnosing and fixing this issue:

  1. Scan the Vehicle: Utilize a diagnostic scan tool to retrieve the DTC code(s) from your vehicle’s onboard computer. This will help identify the specific code P0679 and any additional codes that may be present.

  2. Inspect the Glow Plug Control Module and Wiring: Thoroughly inspect the glow plug control module and its associated wiring. Look for any signs of physical damage, loose connections, or corrosion. Repair or replace any faulty components as necessary.

  3. Test Glow Plug Resistance: Use a multimeter to test the resistance of each glow plug. Compare the readings to the manufacturer’s specifications. Replace any glow plugs that deviate from the recommended range.

  4. Check ECM Functionality: If all previous steps fail to resolve the issue, it may be necessary to inspect the engine control module (ECM). Perform a comprehensive ECM diagnostic to ensure it is functioning correctly. If a faulty ECM is detected, consult a professional mechanic for further guidance.

  5. Clear DTC Codes and Verify Successful Repair: After completing the necessary repairs, clear the DTC codes from the vehicle’s computer memory using a diagnostic scan tool. Perform a test drive to ensure the P0679 DTC code no longer persists and the symptoms have been resolved.

Frequently Asked Questions:

Q1: Can I continue driving with the P0679 DTC code?

A1: While you may be tempted to continue driving with the code, it is not recommended. Ignoring the P0679 DTC code can lead to potential engine damage and increased repair costs. It is advisable to have the issue diagnosed and resolved by a qualified automotive professional.

Q2: How much does it cost to repair the P0679 DTC code?

A2: The cost of repairing the P0679 DTC code can vary depending on the root cause and the labor rates in your area. Generally, the repair cost may involve replacing the glow plug control module or individual glow plugs, along with any necessary wiring repairs. It is best to consult with a mechanic to obtain an accurate estimate tailored to your specific vehicle.

Q3: Can I fix the P0679 DTC code myself?

A3: While some basic troubleshooting steps can be performed by vehicle owners, diagnosing and fixing the P0679 DTC code often requires specialized diagnostic tools and technical knowledge. It is recommended to seek assistance from a professional mechanic who is experienced in diagnosing and repairing DTC codes.

This comprehensive guide has provided an in-depth understanding of the P0679 DTC code, its causes, symptoms, diagnosis, and solutions. By addressing this issue promptly, you can ensure optimal performance and prolonged lifespan of your vehicle’s glow plug system and related circuits.

About author


Meet Sam Mitchell, your experienced and reliable guide in the complex world of car fault codes. With a robust career spanning over 15 years as a professional car mechanic, John has the skills, knowledge, and practical experience to help you navigate car fault issues with confidence.


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