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Engine-Codes – Generic – P0678

P0678 Code - Cylinder 8 Glow Plug Circuit Fault

Quick Answer

The diagnostic trouble code P0678 indicates a fault in the cylinder 8 glow plug circuit. Common causes include Faulty glow plug in cylinder 8, Wiring issues or electrical connections related to the glow plug circuit, Faulty glow plug relay. 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 indicates Cylinder 8 Glow Plug Circuit Fault.
Common causes
Common causes include Faulty glow plug in cylinder 8, Wiring issues or electrical connections related to the glow plug circuit, Faulty glow plug relay.
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 Aug 19, 2024
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Code P0678 Description

The diagnostic trouble code P0678 indicates a fault in the cylinder 8 glow plug circuit. Glow plugs are crucial for diesel engines as they heat up the combustion chamber for easier cold starts. In this case, the code specifically points to an issue in the circuit related to the glow plug in cylinder 8. When this circuit malfunctions, it can lead to difficulties starting the engine, reduced fuel efficiency, increased emissions, and potential engine misfires. If left unaddressed, the issue can cause further damage to the engine and other components.

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

Common Causes of P0678

  1. Faulty glow plug in cylinder 8
  2. Wiring issues or electrical connections related to the glow plug circuit
  3. Faulty glow plug relay
  4. Corrosion or poor connections in the circuit
  5. Engine control module (ECM) malfunction

Symptoms of P0678

  1. Hard starting or extended cranking time
  2. Engine misfires or rough idling
  3. Decreased fuel efficiency
  4. Illuminated check engine light
  5. Increased smoke emissions

How to Fix P0678

  1. Begin by diagnosing the specific cause of the fault, such as testing the glow plug, checking the wiring, and inspecting the relay.
  2. Replace the faulty glow plug in cylinder 8 if necessary.
  3. Repair or replace any damaged wiring or connectors in the glow plug circuit.
  4. Test the glow plug relay and replace it if found to be faulty.
  5. Clear the diagnostic trouble codes and test the vehicle to ensure the issue is resolved.

Cost to Fix P0678

The typical repair costs for addressing a cylinder 8 glow plug circuit fault can range from $150 to $300, including parts and labor. However, the actual cost may vary depending on the location, vehicle make and model, and the specific repair shop. It's recommended to inquire about diagnostic and labor rates at local auto repair shops for a more accurate estimate.

What does this mean?

Tech Notes for P0678









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When is the Code Detected?

The Engine Control Module (ECM) has detected a fault in the cylinder #8 glow plug circuit

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Code P0678 Information for Specific Makes

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.

Frequently Asked Questions about P0678 Code

1. What does OBDII code P0678 mean?

P0678 indicates a fault in the glow plug circuit for cylinder 8, which may prevent the glow plug from heating properly during cold starts.

2. What are the symptoms of code P0678?

Symptoms include difficulty starting the engine in cold weather, rough idling, increased exhaust smoke, and potentially reduced engine performance.

3. What causes the P0678 code?

Common causes include a faulty glow plug, bad glow plug relay, damaged wiring or connectors, or a malfunctioning powertrain control module (PCM).

4. Can I drive with the P0678 code?

Yes, but it’s not recommended for extended periods, especially in cold weather, as it may lead to poor starting conditions and potential engine damage.

5. How do I diagnose code P0678?

Start by inspecting the glow plug, wiring, and connectors for cylinder 8. Use a multimeter to check for continuity and proper resistance in the glow plug circuit.

6. How do I fix the P0678 code?

Repairs may include replacing a faulty glow plug, repairing damaged wiring or connectors, replacing the glow plug relay, or updating/replacing the PCM if necessary.

7. How much does it cost to fix code P0678?

Repair costs vary, but replacing a glow plug typically costs $50-$150, while more extensive electrical repairs or PCM replacement can cost significantly more.

8. Can a bad battery cause the P0678 code?

Yes, a weak or failing battery can prevent proper voltage delivery to the glow plug circuit, potentially triggering the code.

9. Do I need to replace all glow plugs if one fails?

It’s not mandatory, but replacing all glow plugs at the same time is often recommended for consistent performance and reliability.

10. Can a P0678 code cause engine damage?

While the code itself doesn’t directly cause damage, prolonged issues with the glow plug circuit can result in hard starts and increased engine stress, potentially leading to other problems.

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