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Engine-Codes – GMC – P066C GMC

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

Quick Answer

The P066C diagnostic trouble code (DTC) for GMC vehicles 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, such as a loose connection or damaged wiring harness, 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 GMC indicates Cylinder 2 Glow Plug Control Circuit Low Voltage.
Common causes
Common causes include Faulty glow plug in cylinder 2, Wiring issues, such as a loose connection or damaged wiring harness, 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 12, 2024
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Code P066C GMC Description

The P066C diagnostic trouble code (DTC) for GMC vehicles indicates an issue with the Cylinder 2 Glow Plug Control Circuit experiencing low voltage. Glow plugs are essential components in diesel engines that aid in cold starting by heating the air-fuel mixture in the combustion chamber. When the engine is cold, the glow plugs heat up to ensure proper combustion of the air-fuel mixture. In this case, the control circuit for the glow plug in cylinder 2 is not receiving sufficient voltage, which can lead to difficulties in starting the engine, reduced performance, and increased emissions.

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

Common Causes of P066C GMC

  1. Faulty glow plug in cylinder 2.
  2. Wiring issues, such as a loose connection or damaged wiring harness.
  3. Malfunctioning glow plug control module.
  4. Electrical system problems, such as a blown fuse or faulty relay.
  5. Corrosion or debris affecting the glow plug connection.

Symptoms of P066C GMC

  1. Difficulty starting the engine, especially in cold weather.
  2. Rough idle or misfiring during start-up.
  3. Reduced fuel efficiency.
  4. Engine hesitation or lack of power.
  5. Illumination of the check engine light.

How to Fix P066C GMC

  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 wiring harness and connections for any signs of damage or corrosion, repairing or replacing as necessary.
  3. Test the glow plug in cylinder 2 to determine if it is functioning correctly and replace it if found faulty.
  4. Check the glow plug control module for proper operation and replace if deemed defective.
  5. Clear the DTC and perform a test drive to ensure the issue has been resolved.

Cost to Fix P066C GMC

The typical repair costs for addressing a P066C GMC code can range from $100 to $300, depending on the specific cause of the issue and the price of parts. This estimate includes the cost of parts such as a new glow plug, wiring harness, or control module, as well as labor charges. It's important to note that diagnostic time and labor rates at auto repair shops can vary, so it's advisable to check with local shops for a more accurate estimate. Additionally, rates may be higher at dealerships or in metropolitan areas, while independent shops often offer more affordable prices.

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Information for Specific GMC Models

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 GMC Code

1. What does the OBDII code P066C mean for a GMC vehicle?

The P066C code indicates a low voltage issue in the glow plug control circuit for cylinder 2 in a GMC vehicle.

2. What are the common symptoms of the P066C code?

Symptoms may include difficulty starting the engine in cold weather, a check engine light, rough idling, or reduced engine performance.

3. What causes the P066C code to appear?

The code can be caused by a faulty glow plug, damaged wiring or connectors, a malfunctioning glow plug control module, or a weak vehicle battery.

4. Can driving with the P066C code damage my GMC vehicle?

Driving with this code may cause poor engine performance in cold weather and could eventually lead to further damage if left unresolved.

5. How do I diagnose the P066C code in my GMC vehicle?

Diagnosis involves checking the glow plug, inspecting the wiring and connectors for damage, and testing the glow plug control module with a multimeter.

6. How can I fix the P066C code?

Repairs may include replacing the faulty glow plug, repairing damaged wiring or connectors, or replacing the glow plug control module if necessary.

7. How much does it cost to fix the P066C code in a GMC?

The repair cost depends on the issue but typically ranges from $100 to $300 for parts and labor, depending on whether the glow plug or control module needs replacement.

8. Can a weak battery trigger the P066C code?

Yes, a weak or failing battery can cause low voltage issues in the glow plug control circuit, potentially triggering this code.

9. Will clearing the code with a scanner fix the issue?

Clearing the code may temporarily turn off the check engine light, but the underlying issue must be resolved to prevent the code from returning.

10. Can I replace the glow plug for cylinder 2 myself?

If you have basic mechanical knowledge and the proper tools, you can replace the glow plug yourself, but professional diagnosis is recommended to ensure accurate repairs.

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