P0678 2014 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 2014 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 2014 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 2014 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 2014 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 2014 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 2014 GMC Sierra Code
What does the OBDII code P0678 mean on a 2014 GMC Sierra?
P0678 indicates a fault in the glow plug circuit for cylinder 8, meaning the engine control module (ECM) has detected an issue with the electrical circuit or performance of the glow plug in that specific cylinder.
What are the common symptoms of a P0678 code on a 2014 GMC Sierra?
Symptoms may include difficulty starting the engine in cold weather, rough idle during cold starts, reduced fuel efficiency, and the illumination of the check engine light.
What causes the P0678 code to appear on a 2014 GMC Sierra?
Common causes include a faulty glow plug in cylinder 8, damaged or corroded wiring or connectors in the glow plug circuit, a defective glow plug control module, or issues with the ECM.
How do you diagnose a P0678 code on a 2014 GMC Sierra?
Diagnosis typically involves visually inspecting the glow plug and its wiring, testing the resistance of the glow plug, checking for voltage at the glow plug connector, and using a scan tool to monitor related data.
Can you drive with a P0678 code on a 2014 GMC Sierra?
While the vehicle may still run, driving with a P0678 code is not recommended, especially in cold weather, as it can lead to hard starting and potential engine damage over time.
How can you fix the P0678 code on a 2014 GMC Sierra?
Repairs may include replacing the faulty glow plug, repairing or replacing damaged wiring or connectors, replacing the glow plug control module, or reprogramming the ECM if necessary.
How much does it cost to repair a P0678 code on a 2014 GMC Sierra?
The cost depends on the specific issue but typically ranges from $100 to $300 for parts and labor, with glow plug replacement being a common repair.
Does the P0678 code always require a glow plug replacement?
No, the issue could also stem from a wiring problem, faulty connectors, or a malfunctioning glow plug control module, so proper diagnosis is essential.
What tools are needed to troubleshoot a P0678 code on a 2014 GMC Sierra?
You may need a digital multimeter, a scan tool or OBDII code reader, and basic hand tools to test and replace components in the glow plug circuit.
Can a P0678 code return after being fixed on a 2014 GMC Sierra?
Yes, if the root cause isn’t fully addressed, such as intermittent wiring issues or control module problems, the code can reappear.
Discuss the causes and fixes for P0678 2014 GMC Sierra OBDII Code
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