P0677 2015 GMC Sierra Code - Cylinder 7 Glow Plug Circuit Fault
Quick Answer
n the diesel engine, air alone is compressed in the cylinder. Common causes include Faulty cylinder #7 glow plug, Cylinder #7 glow plug harness is open or shorted, Cylinder #7 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
- P0677 2015 GMC Sierra indicates Cylinder 7 Glow Plug Circuit Fault.
- Common causes
- Common causes include Faulty cylinder #7 glow plug, Cylinder #7 glow plug harness is open or shorted, Cylinder #7 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 P0677 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 P0677 2015 GMC Sierra?
- Faulty cylinder #7 glow plug
- Cylinder #7 glow plug harness is open or shorted
- Cylinder #7 glow plug circuit poor electrical connection
- Faulty Glow Plug Control Module (GPCM)
How to Fix the DTC P0677 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 P0677 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 P0677 2015 GMC Sierra Code
1. What does the OBDII code P0677 mean on a 2015 GMC Sierra?
P0677 indicates a fault in the glow plug circuit for cylinder 7, suggesting the glow plug or its related components are malfunctioning.
2. What are the symptoms of code P0677 in a 2015 GMC Sierra?
Common symptoms include difficulty starting the engine in cold weather, rough idling, reduced fuel efficiency, and an illuminated check engine light.
3. What causes the P0677 code to appear?
The code can be triggered by a faulty glow plug, damaged glow plug wiring, a failed glow plug control module, or poor electrical connections in the circuit.
4. Can I drive my 2015 GMC Sierra with the P0677 code?
While the truck may still be drivable, continued operation can lead to harder starts and potential damage to the engine or emissions components if left unaddressed.
5. How do I diagnose the P0677 code on my truck?
Diagnosis involves scanning for codes, testing the cylinder 7 glow plug for functionality, inspecting the wiring and connectors, and checking the glow plug module for faults.
6. How do I fix the P0677 code on a 2015 GMC Sierra?
Repairs may include replacing the faulty glow plug, repairing damaged wiring, cleaning or securing electrical connections, or replacing the glow plug control module.
7. How much does it cost to fix the P0677 code?
The cost varies but typically includes $20–$50 for a glow plug and $100–$300 for labor, depending on the shop and region.
8. Can a bad glow plug cause engine damage on a 2015 GMC Sierra?
A single bad glow plug usually won't cause immediate damage but can lead to poor starting and increased strain on the engine, potentially causing long-term issues.
9. How can I prevent the P0677 code from recurring?
Regular maintenance, including inspecting the glow plugs and wiring for damage or corrosion, can help prevent this code from reappearing.
10. Does the P0677 code affect emissions compliance?
Yes, a fault in the glow plug system can affect the engine’s combustion process, potentially leading to higher emissions and failure of an emissions test.
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