P066A GMC Code - Cylinder 1 Glow Plug Control Circuit Low Voltage
Quick Answer
n the diesel engine, air alone is compressed in the cylinder. Common causes include Faulty cylinder #1 glow plug, Cylinder #1 glow plug harness is open or shorted, Cylinder #1 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
- P066A GMC indicates Cylinder 1 Glow Plug Control Circuit Low Voltage.
- Common causes
- Common causes include Faulty cylinder #1 glow plug, Cylinder #1 glow plug harness is open or shorted, Cylinder #1 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 P066A 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 P066A GMC?
- Faulty cylinder #1 glow plug
- Cylinder #1 glow plug harness is open or shorted
- Cylinder #1 glow plug circuit poor electrical connection
- Faulty Glow Plug Control Module
How to Fix the DTC P066A 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 P066A 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.
Need more information about the P066A GMC code?
Need more information on how to fix the P066A GMC code? Get Access to Factory Service Manuals
Need Help with the Code?
Get the P066A GMC code diagnosed by a professional: Find a repair shop in your area
Information for Specific GMC Models
- P066A 2014 GMC Sierra — Cylinder 1 Glow Plug Control Circuit Low Voltage
- P066A 2015 GMC Sierra — Cylinder 1 Glow Plug Control Circuit Low Voltage
- P066A 2016 GMC Sierra — Cylinder 1 Glow Plug Control Circuit Low Voltage
- P066A 2017 GMC Sierra — Cylinder 1 Glow Plug Control Circuit Low Voltage
- P066A 2018 GMC Sierra — Cylinder 1 Glow Plug Control Circuit Low Voltage
Frequently Asked Questions about P066A GMC Code
1. What does the OBDII code P066A mean on a GMC vehicle?
The code P066A on a GMC indicates a "Cylinder 1 Glow Plug Control Circuit Low Voltage," meaning the voltage to the glow plug circuit for cylinder 1 is below the expected range.
2. What are the symptoms of the P066A code on a GMC?
Common symptoms include difficulty starting the engine in cold weather, rough idling, reduced engine performance, and an illuminated check engine light.
3. What causes the P066A code on a GMC?
Causes may include a faulty glow plug, damaged wiring or connectors in the glow plug circuit, a failed glow plug control module, or a blown fuse.
4. Can I drive my GMC with the P066A code?
While your GMC may still be drivable, it could experience difficulty starting and reduced performance, especially in cold weather. It's best to address the issue promptly to avoid further complications.
5. How is the P066A code diagnosed?
A mechanic will use an OBDII scanner to confirm the code, inspect the glow plug circuit wiring and connectors, test the glow plug resistance, and check the glow plug control module for proper operation.
6. What repairs are needed to fix the P066A code?
Repairs may include replacing the faulty glow plug, repairing or replacing damaged wiring, cleaning corroded connectors, or replacing the glow plug control module if it's defective.
7. How much does it cost to fix the P066A code on a GMC?
Repair costs vary but may range from $100 to $300 for parts and labor, depending on whether the glow plug, wiring, or control module needs replacement.
8. Can a bad glow plug cause other issues besides the P066A code?
Yes, a bad glow plug can lead to hard starting, increased emissions, and poor engine performance, particularly in colder climates.
9. How can I prevent the P066A code from returning on my GMC?
Regular maintenance, including inspecting and replacing glow plugs as needed, checking the wiring for damage, and ensuring the glow plug control module is functioning correctly, can help prevent the code.
10. Will clearing the P066A code with a scanner fix the problem?
Clearing the code will remove the check engine light temporarily, but the underlying issue must be resolved to prevent the code from returning.
Discuss the causes and fixes for P066A GMC OBDII Code
Code P066A GMC comments
No comments found for this page.
Fix Your Car Smarter
Try the New AutoCodes App!
Get complete OBDII diagnostics, repair solutions, and cost estimates, plus AI chat support on demand.
