P0307 GMC Code - Cylinder 7 Misfire Detected
Quick Answer
The P0307 GMC code indicates that a misfire has been detected in cylinder 7 of the vehicle's engine. Common causes include Faulty spark plug in cylinder 7, Failing ignition coil in cylinder 7, Clogged fuel injector in cylinder 7. 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
- P0307 GMC indicates Cylinder 7 Misfire Detected.
- Common causes
- Common causes include Faulty spark plug in cylinder 7, Failing ignition coil in cylinder 7, Clogged fuel injector in cylinder 7.
- 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.
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Code P0307 GMC Description
The P0307 GMC code indicates that a misfire has been detected in cylinder 7 of the vehicle's engine. This means that the fuel in that particular cylinder did not ignite properly, causing a disruption in the combustion process. This issue can lead to a rough idle, decreased engine performance, reduced fuel efficiency, and potentially even engine damage if left unresolved. Misfires can be caused by a variety of factors, including ignition system problems, fuel delivery issues, vacuum leaks, or mechanical problems within the engine.
Common Causes of P0307 GMC
- Faulty spark plug in cylinder 7
- Failing ignition coil in cylinder 7
- Clogged fuel injector in cylinder 7
- Vacuum leak near cylinder 7
- Low compression in cylinder 7
Symptoms of P0307 GMC
- Rough idle
- Loss of power during acceleration
- Increased fuel consumption
- Engine vibration
- Illuminated check engine light
How to Fix P0307 GMC
- Perform a comprehensive diagnostic to identify the specific cause of the misfire in cylinder 7.
- Replace the spark plug in cylinder 7 if it is found to be faulty.
- Test and potentially replace the ignition coil in cylinder 7 if necessary.
- Clean or replace the fuel injector in cylinder 7 if it is clogged.
- Address any vacuum leaks near cylinder 7 and repair as needed.
Cost to Fix P0307 GMC
The typical repair costs for a cylinder misfire can range from $100 to $500, depending on the specific cause and parts needed. This estimate includes parts and labor. Keep in mind that diagnostic time and labor rates can vary, so it's recommended to get a quote from a local auto repair shop for a more accurate estimate.
Tech Notes for P0307 GMC
There is a Factory Service Bulletins for All 2000-2020 GMC Models:
2000-2020 GMC Factory Service Bulletin OBDII Code P0307
This Factory Service Bulletin explains how this condition may be caused by significant carbon build-up on the intake and/or exhaust valves due to fuel contamination or incomplete burning of the fuel.
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Information for Specific GMC Models
- P0307 2014 GMC Sierra — Cylinder 7 Misfire Detected
- P0307 2015 GMC Sierra — Cylinder 7 Misfire Detected
- P0307 2016 GMC Sierra — Cylinder 7 Misfire Detected
- P0307 2017 GMC Sierra — Cylinder 7 Misfire Detected
- P0307 2018 GMC Sierra — Cylinder 7 Misfire Detected
Frequently Asked Questions about P0307 GMC Code
No Frequently Asked Questions about P0307 GMC Code found.
Discuss the causes and fixes for P0307 GMC OBDII Code
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Change all spark plugs and thought it was the coil but it wasn't the Code is still 307 took it to garage they said it was Number 7 Cycling was not moving said we had to do the Head and number 7 Cycliner what do you think thanks so muy
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If you already replaced the plugs and ruled out the coil, you’re doing the right things. But I would be careful jumping straight to “needs a head” without a few key checks first.
When a shop says the cylinder is “not moving,” they usually mean that cylinder is not contributing — but that can be caused by several things, not just internal engine damage.
Before tearing into the engine, I would want to confirm:
• Compression test or leak-down test on cylinder 7
If compression is low, then yes — you could be looking at a valve issue, lifter problem, or something mechanical in the head.• Fuel injector check
A dead or clogged injector on cylinder 7 will cause a misfire and can make it seem like the cylinder isn’t working at all.• Lifter/cam issue (very common on GM V8s)
On many GMC/Chevy V8 engines, especially with AFM/DOD, lifters can collapse or cam lobes can wear down. That will cause a dead cylinder and often gets mistaken for a “head problem.”• Scan data for misfire counts and fuel trims
This helps confirm whether it’s fuel, ignition, or mechanical.If compression is good, it’s not a head problem — then you’re looking at injector or valvetrain control.
If compression is low, then yes, the next step is figuring out why (valve not sealing, lifter not opening the valve, etc.) before committing to major work.
Bottom line:
Don’t approve a head job until a compression or leak-down test clearly shows a mechanical failure. A lot of cylinder 7 misfires on these engines end up being lifters or injectors, not the entire head.
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