AutoCodes – GMC – P0306 GMC

P0306 GMC Code - Cylinder 6 Misfire Detected

Quick Answer

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. Common causes include Faulty spark plug 6, Clogged or faulty fuel injector 6, Faulty ignition coil 6. 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: P0306 GMC indicates Cylinder 6 Misfire Detected.
Common causes: Common causes include Faulty spark plug 6, Clogged or faulty fuel injector 6, Faulty ignition coil 6.
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 42,462

How popular is this code, among other codes? Medium

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
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
FAQs
Comments
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Code P0306 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 P0306 GMC - Cylinder 6 Misfire Detected - AutoCodes.com — P0306 GMC Code - Cylinder 6 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0306 GMC?

Faulty spark plug 6
Clogged or faulty fuel injector 6
Faulty ignition coil 6
Fuel injector 6 harness is open or shorted
Fuel injector 6 circuit poor electrical connection
Ignition coil 6 harness is open or shorted
Ignition coil 6 circuit poor electrical connection
Insufficient cylinder 6 compression
Incorrect fuel pressure
Intake air leak

How to Fix the DTC P0306 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 P0306 code means that cylinder 6 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 6. 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 P0306
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 P0306 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 P0306 GMC code?

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Need Help with the Code?

Get the P0306 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P0306 2014 GMC Sierra — Cylinder 6 Misfire Detected
P0306 2015 GMC Sierra — Cylinder 6 Misfire Detected
P0306 2016 GMC Sierra — Cylinder 6 Misfire Detected
P0306 2017 GMC Sierra — Cylinder 6 Misfire Detected
P0306 2018 GMC Sierra — Cylinder 6 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 P0306 GMC Code

1. What are common symptoms of OBDII code P0306 (Cylinder 6 Misfire Detected)?

Symptoms may include rough idling, loss of power, engine vibration, and potential hesitation or stalling while driving.

2. What are the possible causes of a Cylinder 6 misfire in a GMC vehicle?

Common causes of a Cylinder 6 misfire can include faulty spark plugs, ignition coil issues, fuel injector problems, vacuum leaks, or low compression in the cylinder.

3. How can I diagnose the cause of a Cylinder 6 misfire in my GMC vehicle?

Diagnosis typically involves inspecting spark plugs, ignition coils, fuel injectors, and checking for vacuum leaks. Compression testing may also be necessary to rule out internal engine issues.

4. Can a dirty fuel injector cause a Cylinder 6 misfire?

Yes, a dirty or clogged fuel injector can disrupt the fuel flow to the cylinder, leading to a misfire condition.

5. What are some tips for repairing OBDII code P0306 in a GMC vehicle?

Start by checking and replacing spark plugs, ignition coils, and fuel injectors if necessary. Ensure proper engine compression and address any vacuum leaks. Reset the code after making repairs and test drive to confirm the issue is resolved.

6. Is it safe to continue driving with OBDII code P0306 (Cylinder 6 Misfire Detected) in my GMC vehicle?

It is not recommended to drive with a misfire as it can lead to further engine damage. Address the issue promptly to prevent more serious problems.

7. Can bad ignition coils cause a Cylinder 6 misfire?

Yes, faulty ignition coils can result in a weak or inconsistent spark, leading to a misfire in Cylinder 6.

8. How important is it to address a Cylinder 6 misfire promptly?

Addressing a misfire promptly is crucial to prevent damage to the catalytic converter, oxygen sensors, and other engine components. Ignoring the issue can lead to more costly repairs down the line.

9. Can a faulty oxygen sensor trigger OBDII code P0306 in a GMC vehicle?

While a faulty oxygen sensor itself may not directly cause a Cylinder 6 misfire, it can contribute to an imbalance in fuel mixture, potentially leading to a misfire condition.

10. Will a simple tune-up resolve OBDII code P0306 in a GMC vehicle?

A basic tune-up, including replacing spark plugs and filters, may help resolve a Cylinder 6 misfire if the issue is related to worn components. However, a thorough diagnosis may be needed for more complex cases.