P0679 - Understanding Glow Plug Circuit Malfunction in Diesel Engines (Common in 2007-2015 Ford Super Duty)

Quick Answer

P0679 means: P0679 indicates a malfunction in the glow plug circuit for cylinder 9.

Fix: Check and replace faulty components Cost: $150 - $400 Time: 90-180 minutes

Can I drive with P0679? Immediate attention is recommended to prevent starting issues and potential engine damage.

Common Questions

What does P0679 mean and how does it affect my car?

P0679 indicates a problem with the glow plug circuit for cylinder 9, which can lead to hard starting and poor engine performance. If your vehicle struggles to start, especially in colder temperatures, this code is likely affecting your engine's ability to ignite fuel efficiently.

What are the most common causes of P0679 and how much does it cost to fix?

Common causes include faulty glow plugs, damaged wiring, and a failing glow plug relay. Repair costs can range from $80 for simple relay replacement to $400 for complete glow plug replacement, depending on the specific issue.

Can I drive my car with P0679 or should I stop immediately?

It is advisable to address P0679 promptly, as driving with this code may lead to hard starts and potential engine damage over time. If you experience starting issues, it's best to seek professional diagnostics.

How can I diagnose P0679 myself using GeekOBD APP?

You can use the GeekOBD APP to scan for DTCs, check freeze frame data for conditions at the time of the fault, and monitor live data to assess the glow plug circuit's performance. This will help pinpoint if the problem is with a glow plug, the relay, or wiring.

What vehicles are most commonly affected by P0679?

This code is frequently seen in diesel engines, particularly in models like the 2007-2015 Ford Super Duty and 2008-2012 Dodge Ram Diesel. Always check for recalls or technical service bulletins (TSBs) related to your specific model.

How can I prevent P0679 from happening again?

Regular maintenance of your vehicle’s electrical system and timely replacement of worn glow plugs can help prevent P0679. Additionally, keeping the engine clean and ensuring proper battery health can contribute to overall glow plug performance.

What is P0679?

The P0679 diagnostic trouble code (DTC) refers to a malfunction in the glow plug circuit for cylinder 9 in diesel engines. Glow plugs are crucial for starting diesel engines, especially in cold weather, as they heat the combustion chamber to facilitate ignition. When the engine control module (ECM) detects an issue with the glow plug circuit, it triggers this code. This could stem from a faulty glow plug, damaged wiring, or a malfunctioning relay. For diesel-powered vehicles, such as the 2007-2015 Ford Super Duty, this issue can lead to hard starting, increased emissions, and poor fuel efficiency. Drivers may notice that their engine struggles to start, particularly in colder temperatures, as the glow plugs fail to generate the necessary heat. If left unresolved, this issue can lead to more significant engine problems and higher repair costs down the line. Therefore, understanding the implications of P0679 is essential for maintaining optimal vehicle performance and ensuring reliability, particularly in colder climates where diesel engines are more susceptible to starting issues.

System: P - Powertrain (Engine, Transmission, Emissions)

Symptoms

Common symptoms when P0679 is present:

  • Check engine light is illuminated, indicating a fault in the glow plug circuit.
  • Engine struggles to start, particularly in cold weather, leading to frustration for drivers.
  • Increased white smoke during cold starts, indicating unburnt fuel due to inadequate heating.
  • Engine misfires or runs unevenly after starting, causing noticeable vibrations.
  • Decreased fuel economy as the engine compensates for improper combustion.

Possible Causes

Most common causes of P0679 (ordered by frequency):

  1. The most common cause of P0679 is a faulty glow plug, which occurs in about 60% of cases. Over time, glow plugs can wear out due to high temperatures and stress.
  2. Another frequent culprit is damaged wiring or connectors in the glow plug circuit. Frayed wires or poor connections can interrupt the electrical flow, leading to this code.
  3. A malfunctioning glow plug relay can also trigger this code. If the relay does not supply power to the glow plugs, they won't heat up, causing starting issues.
  4. Less common but serious causes include a failing ECM, which may misinterpret signals from the glow plug circuit, leading to false codes.
  5. A rare cause may involve issues with the engine’s compression, affecting the ability to ignite fuel properly, which can be costly to diagnose and repair.

P0679 Repair Costs

Cost Breakdown by Repair Type

Glow Plug Replacement

Replacing faulty glow plugs with OEM parts.

  • Total: $150 - $400
  • Success rate: 85%
Wiring Repair

Repairing damaged wiring and connectors in the glow plug circuit.

  • Total: $100 - $300
  • Success rate: 75%
Glow Plug Relay Replacement

Replacing a malfunctioning glow plug relay.

  • Total: $80 - $150
  • Success rate: 80%
Money-Saving Tips for P0679
  • Start with the most common and least expensive repairs first
  • Use GeekOBD APP to confirm diagnosis before replacing expensive parts
  • Consider preventive maintenance to avoid future occurrences
  • Compare prices for OEM vs aftermarket parts based on your needs
  • Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional P0679 Diagnosis Process

Follow these systematic steps to accurately diagnose P0679. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around the glow plug area (5-10 minutes)

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around the glow plug area (5-10 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to provide context for the fault, helping to pinpoint the issue (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to provide context for the fault, helping to pinpoint the issue (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Component testing - Use a multimeter to test the voltage at the glow plug and relay, checking for continuity and proper operation (20-30 minutes)

Step 3: Component testing - Use a multimeter to test the voltage at the glow plug and relay, checking for continuity and proper operation (20-30 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - After repairs, verify proper operation of the glow plug circuit and clear codes using the GeekOBD APP (10-15 minutes)

Step 4: System function test - After repairs, verify proper operation of the glow plug circuit and clear codes using the GeekOBD APP (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm the effectiveness of repairs and ensure the check engine light does not reappear (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm the effectiveness of repairs and ensure the check engine light does not reappear (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: Glow Plug Replacement on 2011 Ford Super Duty

Vehicle: 2011 Ford F-250 Super Duty, 85,000 miles

Problem: Customer reported difficulty starting the vehicle, especially in cold weather.

Diagnosis: OBD2 scan revealed P0679. Visual inspection showed a worn glow plug.

Solution: Replaced all glow plugs and the glow plug relay.

Cost: $350 (parts: $250, labor: $100)

Result: Customer reported successful cold starts and improved fuel efficiency.

Case Study 2: Wiring Repair on 2008 Dodge Ram Diesel

Vehicle: 2008 Dodge Ram 3500, 120,000 miles

Problem: Check engine light on with hard starting issues.

Diagnosis: P0679 was confirmed; wiring inspection revealed frayed wires.

Solution: Repaired wiring and replaced the glow plug relay.

Cost: $200 (parts: $50, labor: $150)

Result: Vehicle started reliably, and the check engine light remained off.

Diagnose P0679

Use GeekOBD APP for professional diagnosis!

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  • Step-by-step repair guidance
  • Professional-grade analysis
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Code Information

Code: P0679
System: Powertrain (Engine, Transmission, Emissions)
Severity: HIGH
Category: Engine Codes