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Engine-Codes – GMC – P0678 GMC

P0678 GMC Code - Cylinder 8 Glow Plug Circuit Fault

Quick Answer

The P0678 GMC code indicates a fault in the glow plug circuit for cylinder 8 in the vehicle's engine. Common causes include Faulty glow plug in cylinder 8, Damaged or corroded wiring in the glow plug circuit, Malfunctioning glow plug control module. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0678 GMC indicates Cylinder 8 Glow Plug Circuit Fault.
Common causes
Common causes include Faulty glow plug in cylinder 8, Damaged or corroded wiring in the glow plug circuit, Malfunctioning glow plug control module.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 12, 2024
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Code P0678 GMC Description

The P0678 GMC code indicates a fault in the glow plug circuit for cylinder 8 in the vehicle's engine. Glow plugs are used in diesel engines to heat the combustion chamber for easier starting in cold conditions. When this code is triggered, it means that there is an issue with the electrical circuit that controls the glow plug in cylinder 8. This can lead to difficulties in starting the engine, reduced fuel efficiency, rough idling, and potentially even engine misfires.

OBDII Code P0678 GMC - Cylinder 8 Glow Plug Circuit Fault
P0678 GMC Code - Cylinder 8 Glow Plug Circuit Fault

Common Causes of P0678 GMC

  1. Faulty glow plug in cylinder 8.
  2. Damaged or corroded wiring in the glow plug circuit.
  3. Malfunctioning glow plug control module.
  4. Issues with the engine's computer or sensors.
  5. Poor electrical connections in the circuit.

Symptoms of P0678 GMC

  1. Difficulty starting the engine, especially in cold weather.
  2. Rough idling or a noticeable decrease in engine performance.
  3. Increased fuel consumption.
  4. Engine misfires or hesitation during acceleration.
  5. Check Engine Light illuminated on the dashboard.

How to Fix P0678 GMC

  1. Begin by diagnosing the specific issue causing the glow plug circuit fault using a diagnostic scanner to pinpoint the exact problem.
  2. Inspect the glow plug in cylinder 8 for any signs of damage or wear and replace if necessary.
  3. Check the wiring in the glow plug circuit for any breaks, corrosion, or loose connections and repair as needed.
  4. Test the glow plug control module to ensure it is functioning correctly and replace if faulty.
  5. Clear the diagnostic trouble codes from the vehicle's computer and test the vehicle to ensure the issue has been resolved.

Cost to Fix P0678 GMC

The typical repair costs for a cylinder 8 glow plug circuit fault can range from $150 to $300, depending on the specific parts that need to be replaced and the labor involved. This estimate includes the cost of a new glow plug, wiring repairs, and any necessary diagnostic testing. Keep in mind that labor rates at auto repair shops can vary, so it's advisable to check with local shops for a more accurate estimate based on your vehicle make and model.

What does this mean?

Tech Notes for P0678 GMC









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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

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