AutoCodes – GMC – P0304 2014 GMC Sierra

P0304 2014 GMC Sierra Code - Cylinder 4 Misfire Detected

Quick Answer

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. Common causes include Faulty Spark Plug #4, Clogged or faulty Fuel Injector #4, Faulty Ignition Coil #4. 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: P0304 2014 GMC Sierra indicates Cylinder 4 Misfire Detected.
Common causes: Common causes include Faulty Spark Plug #4, Clogged or faulty Fuel Injector #4, Faulty Ignition Coil #4.
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 466

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
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0304 2014 GMC Sierra 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 P0304 2014 GMC Sierra - Cylinder 4 Misfire Detected - AutoCodes.com — P0304 2014 GMC Sierra Code - Cylinder 4 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0304 2014 GMC Sierra?

Faulty Spark Plug #4
Clogged or faulty Fuel Injector #4
Faulty Ignition Coil #4
Fuel Injector #4 harness is open or shorted
Fuel Injector #4 circuit poor electrical connection
Ignition Coil #4 harness is open or shorted
Ignition Coil #4 circuit poor electrical connection
Insufficient cylinder 4 compression
Incorrect fuel pressure
Intake air leak

How to Fix the DTC P0304 2014 GMC Sierra?

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 P0304 code means that cylinder 4 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 4. 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 Chevrolet Models:
2000-2020 Chevrolet Factory Service Bulletin OBDII Code P0304
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.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0304 2014 GMC Sierra 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.

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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 P0304 2014 GMC Sierra Code

1. What does the OBDII code P0304 mean on a 2014 GMC Sierra?

P0304 indicates a misfire has been detected in cylinder 4 of the engine.

2. What are the common symptoms of a P0304 code in a 2014 GMC Sierra?

Symptoms may include rough idling, decreased engine power, poor fuel economy, hesitation during acceleration, and the check engine light turning on.

3. What causes a P0304 code on a 2014 GMC Sierra?

Common causes include a faulty spark plug, a bad ignition coil, a clogged or faulty fuel injector, low compression in cylinder 4, or intake manifold gasket leaks.

4. Can a dirty fuel injector cause a P0304 code?

Yes, a clogged or malfunctioning fuel injector in cylinder 4 can disrupt the fuel delivery, leading to a misfire and triggering the P0304 code.

5. How do I diagnose a P0304 code on my 2014 GMC Sierra?

Start by inspecting the spark plug, ignition coil, and wiring for cylinder 4. Use a compression tester to check for low compression and scan for any related codes.

6. Can I drive my 2014 GMC Sierra with a P0304 code?

Driving with a P0304 code is not recommended as it can cause further engine damage, such as overheating the catalytic converter or worsening the misfire.

7. How do you fix a P0304 code on a 2014 GMC Sierra?

Repairs may include replacing the spark plug or ignition coil for cylinder 4, cleaning or replacing the fuel injector, repairing vacuum leaks, or addressing low compression issues.

8. How much does it cost to repair a P0304 code on a 2014 GMC Sierra?

Repair costs vary depending on the issue. Replacing a spark plug or ignition coil may cost $50-$300, while fixing low compression or injector issues can be more expensive.

9. Will a P0304 code cause long-term damage if not repaired?

Yes, ignoring a P0304 code can lead to engine damage, such as catalytic converter failure, increased wear on engine components, and reduced overall performance.

10. Can bad fuel cause a P0304 code in a 2014 GMC Sierra?

Yes, contaminated or low-quality fuel can lead to a misfire in cylinder 4, causing the P0304 code. Using high-quality fuel may help prevent this issue.