P068D GMC Code - Cylinder 7 Glow Plug Control Circuit High Voltage
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
- P068D GMC indicates Cylinder 7 Glow Plug Control Circuit High Voltage.
- 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 P068D GMC 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 P068D GMC?
- 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
How to Fix the DTC P068D GMC?
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 P068D GMC 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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Information for Specific GMC Models
- P068D 2014 GMC Sierra — Cylinder 7 Glow Plug Control Circuit High Voltage
- P068D 2015 GMC Sierra — Cylinder 7 Glow Plug Control Circuit High Voltage
- P068D 2016 GMC Sierra — Cylinder 7 Glow Plug Control Circuit High Voltage
- P068D 2017 GMC Sierra — Cylinder 7 Glow Plug Control Circuit High Voltage
- P068D 2018 GMC Sierra — Cylinder 7 Glow Plug Control Circuit High Voltage
Frequently Asked Questions about P068D GMC Code
1. What does the OBDII code P068D mean on a GMC vehicle?
P068D on a GMC indicates a high voltage issue in the Cylinder 7 Glow Plug Control Circuit, which is responsible for controlling the glow plug in that cylinder for optimal combustion during cold starts.
2. What are common symptoms of the P068D code?
Common symptoms include difficulty starting the engine in cold weather, a rough idle, reduced fuel efficiency, and an illuminated check engine light.
3. What causes the P068D code to appear?
The code can be triggered by a faulty glow plug in cylinder 7, damaged wiring or connectors in the glow plug circuit, a malfunctioning glow plug control module, or corrosion on electrical contacts.
4. Can I drive my GMC with the P068D code active?
While you can typically drive with this code, it is not recommended as it can lead to harder starts in cold conditions and may cause long-term damage to the engine or emissions system.
5. How do I diagnose the P068D code on my GMC?
Diagnosis involves inspecting the glow plug in cylinder 7, checking the wiring and connectors for damage or corrosion, and testing the glow plug control module for proper operation.
6. How do I fix the P068D code on my GMC?
Repairs may include replacing the faulty glow plug, repairing or replacing damaged wiring or connectors, cleaning corroded contacts, or replacing the glow plug control module if it is defective.
7. What tools are needed to troubleshoot the P068D code?
You’ll need an OBDII scanner, a multimeter to check electrical continuity, and possibly a torque wrench to remove and install the glow plug.
8. How much does it cost to fix the P068D code on a GMC?
The repair cost varies but typically ranges from $100 to $300, depending on whether the issue is with the glow plug itself or requires more extensive repairs such as module replacement.
9. Can a weak battery cause the P068D code?
Yes, a weak or failing battery can sometimes cause voltage-related issues that may trigger the P068D code, as the glow plug system relies on consistent electrical power.
10. Will clearing the P068D code fix the problem?
Clearing the code will reset the check engine light, but the underlying issue causing the high voltage in the glow plug circuit must be addressed to prevent the code from returning.
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