P0678 2015 GMC Sierra Code - Cylinder 8 Glow Plug Circuit Fault
Quick Answer
n the diesel engine, air alone is compressed in the cylinder. 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 2015 GMC Sierra 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.
Code P0678 2015 GMC Sierra Description
Control of the glow plugs is accomplished by the Glow Plug Control Module. The nominal voltage for the glow plugs is 5.4 volts. When the ignition is turned On, the Glow Plug Control Module applies 7.2 V for 2.2 s, then 5.7 V for 0.8 s, and then 5.4 V until 1200°C (2192°F) is reached. The maximum voltage of the system is 10 V. While the engine is running the voltage will vary between 4.7 - 10 V when in closed loop control to maintain a glow plug temperature that ranges from 1150° - 1180°C (2102° - 2156°F). The temperature and the power consumption are controlled between the Engine Control Module (ECM) and the Glow Plug Control Module within a wide range to suit the engine's pre-heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre - glow times can be kept to a minimum for a short wait to crank times and maximum glow plug durability.
What are the Possible Causes of the DTC P0678 2015 GMC Sierra?
- 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 Control Module (GPCM)
How to Fix the DTC P0678 2015 GMC Sierra?
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 is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0678 2015 GMC Sierra 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.
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Frequently Asked Questions about P0678 2015 GMC Sierra Code
1. What are the common symptoms of OBDII code P0678 in a 2015 GMC Sierra related to the Cylinder 8 Glow Plug Circuit Fault?
- Common symptoms include rough idling, misfires, decreased fuel efficiency, and the illumination of the Check Engine Light.
2. What are the possible causes of OBDII code P0678 in a 2015 GMC Sierra indicating a Cylinder 8 Glow Plug Circuit Fault?
- The code P0678 can be triggered by a faulty glow plug, damaged wiring or connectors in the glow plug circuit, or issues with the glow plug control module.
3. How can I diagnose a Cylinder 8 Glow Plug Circuit Fault in my 2015 GMC Sierra if I suspect OBDII code P0678?
- Diagnose the issue by checking the glow plug resistance, inspecting the wiring and connectors for damage, and testing the glow plug control module for proper functioning.
4. Can I continue driving my 2015 GMC Sierra with OBDII code P0678 related to a Cylinder 8 Glow Plug Circuit Fault?
- It is not recommended to drive the vehicle with a glow plug circuit fault as it can lead to poor engine performance and potential damage. Immediate attention and repair are advised.
5. What are some repair tips for fixing OBDII code P0678 in a 2015 GMC Sierra with a Cylinder 8 Glow Plug Circuit Fault?
- Repair tips include replacing the faulty glow plug, repairing or replacing damaged wiring and connectors, and addressing any issues with the glow plug control module.
6. Is it necessary to clear the OBDII code P0678 after repairing a Cylinder 8 Glow Plug Circuit Fault in a 2015 GMC Sierra?
- Yes, it is important to clear the code using an OBDII scanner after completing the repairs to reset the Check Engine Light and ensure the issue has been resolved.
7. How can I prevent OBDII code P0678 from reoccurring in my 2015 GMC Sierra after fixing the Cylinder 8 Glow Plug Circuit Fault?
- To prevent the code from reoccurring, perform regular maintenance on the glow plug system, check for any signs of wear or damage, and address any underlying issues promptly.
8. Can a DIY enthusiast with basic automotive knowledge repair OBDII code P0678 related to a Cylinder 8 Glow Plug Circuit Fault in a 2015 GMC Sierra?
- While some basic repairs like replacing the glow plug can be done by a DIY enthusiast, diagnosing and repairing complex issues in the glow plug circuit may require professional expertise.
9. Are there any recalls or service bulletins related to OBDII code P0678 in a 2015 GMC Sierra with a Cylinder 8 Glow Plug Circuit Fault?
- It is advisable to check with a GMC dealership or the manufacturer's website for any recalls or service bulletins related to the specific OBDII code P0678 in your vehicle.
10. What is the typical cost of repairing OBDII code P0678 in a 2015 GMC Sierra due to a Cylinder 8 Glow Plug Circuit Fault?
- The cost of repairing OBDII code P0678 can vary depending on the extent of the issue, parts needed, and labor rates. It is recommended to obtain quotes from reputable mechanics or dealerships for an accurate estimate.
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