AutoCodes – Generic – P0678

P0678 Code - Cylinder 8 Glow Plug Circuit Fault

Quick Answer

The glow plug system is used to assist in providing the heat required to begin combustion during cold engine temperatures. Common causes include Faulty cylinder #8 glow plug, Cylinder #8 glow plug harness is open or shorted, Cylinder #8 glow plug circuit poor electrical connection. 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 cylinder #8 glow plug, Cylinder #8 glow plug harness is open or shorted, Cylinder #8 glow plug circuit poor electrical connection.
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.

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Code Popularity 18,047

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jul 18, 2022

Description
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
FAQs
Comments
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Code P0678 Description

The glow plug system is used to assist in providing the heat required to begin combustion during cold engine temperatures. The glow plugs are heated before and during cranking, as well as initial engine operation. The Engine Control Module (ECM) controls the glow plug ON times by monitoring coolant temperature and glow plug voltage. The California Glow Plug system has eight individual glow plug supply circuits between the controller and the glow plugs. If the feedback voltage from the controller to the ECM is not within range, the ECM sets the OBDII code.

OBDII Code P0678 - Cylinder 8 Glow Plug Circuit Fault - AutoCodes.com — P0678 Code - Cylinder 8 Glow Plug Circuit Fault

What does this mean?

What are the Possible Causes of the DTC P0678?

Faulty cylinder #8 glow plug
Cylinder #8 glow plug harness is open or shorted
Cylinder #8 glow plug circuit poor electrical connection
Faulty glow plug module

How to Fix the DTC P0678?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

User Submitted Video

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0678 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0678 code?

Need more information on how to fix the P0678 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0678 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P0678 Audi — Cylinder 8 Glow Plug Circuit Fault
P0678 Chevrolet — Cylinder 8 Glow Plug Circuit Fault
P0678 Ford — Cylinder 8 Glow Plug Circuit Fault
P0678 GMC — Cylinder 8 Glow Plug Circuit Fault
P0678 Volkswagen — Cylinder 8 Glow Plug Circuit Fault

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 itâ€™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?

Itâ€™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 doesnâ€™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.