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Engine-Codes – GMC – P066C 2015 GMC Sierra

P066C 2015 GMC Sierra Code - Cylinder 2 Glow Plug Control Circuit Low Voltage

Quick Answer

The diagnostic trouble code P066C for a 2015 GMC Sierra indicates an issue with the Cylinder 2 Glow Plug Control Circuit experiencing low voltage. Common causes include Faulty glow plug in cylinder 2, Wiring issues or damaged connectors in the glow plug control circuit, Malfunctioning glow plug control module. 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
P066C 2015 GMC Sierra indicates Cylinder 2 Glow Plug Control Circuit Low Voltage.
Common causes
Common causes include Faulty glow plug in cylinder 2, Wiring issues or damaged connectors in the glow plug control circuit, Malfunctioning glow plug control module.
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.
What is this?
Table of contents Created and updated by William Orellana on Sep 26, 2024
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Code P066C 2015 GMC Sierra Description

The diagnostic trouble code P066C for a 2015 GMC Sierra indicates an issue with the Cylinder 2 Glow Plug Control Circuit experiencing low voltage. Glow plugs are essential components in diesel engines, especially during cold starts, as they heat up the combustion chamber to facilitate easier ignition of the fuel. When the control circuit for the glow plug in cylinder 2 is not receiving sufficient voltage, it can lead to difficulties in starting the engine, reduced performance, increased emissions, and potential long-term damage to the engine.

OBDII Code P066C 2015 GMC Sierra - Cylinder 2 Glow Plug Control Circuit Low Voltage
P066C 2015 GMC Sierra Code - Cylinder 2 Glow Plug Control Circuit Low Voltage

Common Causes of P066C 2015 GMC Sierra

  1. Faulty glow plug in cylinder 2.
  2. Wiring issues or damaged connectors in the glow plug control circuit.
  3. Malfunctioning glow plug control module.
  4. Corrosion or poor connections in the electrical system.
  5. Issues with the engine control module (ECM) affecting the glow plug circuit.

Symptoms of P066C 2015 GMC Sierra

  1. Difficulty starting the engine, especially in cold weather.
  2. Rough idling or engine misfires.
  3. Decreased fuel efficiency.
  4. Illumination of the check engine light.
  5. Increased emissions during operation.

How to Fix P066C 2015 GMC Sierra

  1. Begin by diagnosing the specific cause of the low voltage in the cylinder 2 glow plug control circuit using a diagnostic scanner.
  2. Inspect the glow plug in cylinder 2 for any signs of damage or wear and replace if necessary.
  3. Check the wiring and connectors in the glow plug control circuit for any breaks, corrosion, or loose connections. Repair or replace as needed.
  4. Test the glow plug control module and the engine control module for proper functionality. Replace any faulty components.
  5. Clear the diagnostic trouble code from the vehicle's ECM and perform a test drive to ensure the issue has been resolved.

Cost to Fix P066C 2015 GMC Sierra

The typical repair costs for addressing a Cylinder 2 Glow Plug Control Circuit Low Voltage issue in a 2015 GMC Sierra can vary depending on the specific cause of the problem. On average, the parts required for this repair, including a new glow plug, wiring components, or control modules, can range from $100 to $300. Labor costs at an auto repair shop can add an additional $100 to $300, depending on the shop's hourly rates and the complexity of the repair. It's recommended to consult with local auto repair shops for accurate pricing based on your location and vehicle specifics.

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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 P066C 2015 GMC Sierra Code

1. What does OBDII code P066C mean on a 2015 GMC Sierra?

P066C indicates a low voltage issue in the glow plug control circuit for cylinder 2, which is part of the diesel engine's cold-start system.

2. What are the common symptoms of code P066C in a 2015 GMC Sierra?

Symptoms may include difficulty starting in cold weather, poor engine performance, increased emissions, and an illuminated check engine light.

3. What causes the P066C code to appear on a 2015 GMC Sierra?

Common causes include a faulty glow plug, damaged wiring or connectors in the glow plug circuit, a failed glow plug control module, or a weak battery.

4. How can I diagnose the P066C code in my 2015 GMC Sierra?

Start by inspecting the wiring and connectors for damage or corrosion, testing the glow plug for cylinder 2, and checking the voltage output from the glow plug control module.

5. Can I drive my 2015 GMC Sierra with the P066C code?

While the truck may still run, driving with this code can cause poor cold-start performance and increased emissions. It's best to address the issue promptly.

6. How do I fix the P066C code on a 2015 GMC Sierra?

Repairs may include replacing the faulty glow plug, repairing damaged wiring or connectors, or replacing the glow plug control module if it's defective.

7. How much does it cost to repair the P066C code on a 2015 GMC Sierra?

Repair costs vary but typically range from $100 to $300, depending on whether the glow plug or control module needs replacement.

8. Can a weak battery cause the P066C code on a 2015 GMC Sierra?

Yes, a weak or failing battery can result in insufficient voltage to the glow plug circuit, triggering the P066C code.

9. How can I prevent the P066C code from occurring again?

Regular maintenance, including inspecting the glow plugs, wiring, and battery, can help prevent this code from recurring.

10. Do I need a professional mechanic to fix the P066C code on my 2015 GMC Sierra?

While experienced DIYers may handle basic repairs, consulting a professional mechanic is recommended for accurate diagnostics and repairs.

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