AutoCodes – GMC – P0307 GMC

P0307 GMC Code - Cylinder 7 Misfire Detected

Quick Answer

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. Common causes include Faulty spark plug 7, Clogged or faulty fuel injector 7, Faulty ignition coil 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 7, Clogged or faulty fuel injector 7, Faulty ignition coil 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 Popularity 26,855

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 09, 2022

Description
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
Comments
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Code P0307 GMC Description

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. The Engine Control Module (ECM) can detect these variations by closely monitoring the crankshaft position sensor signal. The signals of the camshaft position sensors are used to determine which cylinder is misfiring. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, the Diagnostic Trouble Code (DTC) will be set. Under certain driving conditions, a misfire rate can be high enough to cause the catalytic converter to overheat, damaging the converter. The Malfunction Indicator Lamp (MIL) flashes when the converter is overheating, damaging conditions are present, and the DTC is set. The DTC will be set when the ECM detects a crankshaft rotation speed variation indicating a single-cylinder misfire rate sufficient to cause emissions levels to exceed mandated standards.

OBDII Code P0307 GMC - Cylinder 7 Misfire Detected - AutoCodes.com — P0307 GMC Code - Cylinder 7 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0307 GMC?

Faulty spark plug 7
Clogged or faulty fuel injector 7
Faulty ignition coil 7
Fuel injector 7 harness is open or shorted
Fuel injector 7 circuit poor electrical connection
Ignition coil 7 harness is open or shorted
Ignition coil 7 circuit poor electrical connection
Insufficient cylinder 7 compression
Incorrect fuel pressure
Intake air leak

How to Fix the DTC P0307 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 does this mean?

Code Tech Notes

The P0307 code means that cylinder 7 is misfiring or is randomly misfiring. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder 7. If the problem persists more tests need to be done to diagnose the problem, see "Possible Causes".

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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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0307 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 P0307 GMC code?

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Need Help with the Code?

Get the P0307 GMC code diagnosed by a professional: Find a repair shop in your area

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

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 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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William Propst
Date: March 16, 2026 at 2:47 pm

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

Reply to Comment
- OBDIITech
  Date: March 17, 2026 at 9:44 pm
  
  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.
  
  Reply to Comment