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Engine-Codes – GMC – P0304 2015 GMC Sierra

P0304 2015 GMC Sierra Code - Cylinder 4 Misfire Detected

Quick Answer

When the diagnostic trouble code P0304 appears on a 2015 GMC Sierra, it indicates that a misfire has been detected in cylinder 4 of the engine. Common causes include Faulty spark plug or ignition coil, Clogged or malfunctioning fuel injector, Vacuum leak in the intake manifold. 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 2015 GMC Sierra indicates Cylinder 4 Misfire Detected.
Common causes
Common causes include Faulty spark plug or ignition coil, Clogged or malfunctioning fuel injector, Vacuum leak in the intake manifold.
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.
What is this?
Table of contents Created and updated by William Orellana on Aug 18, 2024
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Code P0304 2015 GMC Sierra Description

When the diagnostic trouble code P0304 appears on a 2015 GMC Sierra, it indicates that a misfire has been detected in cylinder 4 of the engine. This means that the fuel-air mixture in that specific cylinder is not igniting properly, leading to a disruption in the combustion process. This can result in poor engine performance, reduced fuel efficiency, increased emissions, and potential damage to the catalytic converter over time. The misfire can be caused by a variety of issues, such as a faulty spark plug, ignition coil, fuel injector, or even internal engine problems.

OBDII Code P0304 2015 GMC Sierra - Cylinder 4 Misfire Detected
P0304 2015 GMC Sierra Code - Cylinder 4 Misfire Detected

Common Causes of P0304 2015 GMC Sierra

  1. Faulty spark plug or ignition coil
  2. Clogged or malfunctioning fuel injector
  3. Vacuum leak in the intake manifold
  4. Low compression in cylinder 4
  5. Issues with the engine control module (ECM)

Symptoms of P0304 2015 GMC Sierra

  1. Rough idling or shaking while the engine is running
  2. Decreased acceleration and power
  3. Increased fuel consumption
  4. Engine misfiring or stuttering
  5. Illuminated check engine light

How to Fix P0304 2015 GMC Sierra

  1. Begin by checking and replacing the spark plug in cylinder 4.
  2. Inspect the ignition coil for any signs of damage or wear, replacing if necessary.
  3. Test the fuel injector for proper function and clean or replace as needed.
  4. Perform a compression test to check the health of cylinder 4.
  5. If the issue persists, consult a professional mechanic for further diagnosis and potential internal engine repairs.

Cost to Fix P0304 2015 GMC Sierra

The cost of repairing a cylinder 4 misfire in a 2015 GMC Sierra can vary depending on the specific cause of the issue. In general, replacing a spark plug or ignition coil can cost between $50-$200, while a fuel injector replacement may range from $150-$400. A compression test and further diagnostics could add to the total repair cost. Labor rates at auto repair shops can vary, but typically range from $80 to $150 per hour. It's recommended to get a personalized estimate from a local mechanic to determine the exact cost for your specific situation.

What does this mean?

Tech Notes for P0304 2015 GMC Sierra

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.

Need more information about the P0304 2015 GMC Sierra code?

Need more information on how to fix the P0304 2015 GMC Sierra code? Get Access to Factory Service Manuals

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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 2015 GMC Sierra Code

1. What does the OBDII code P0304 mean on a 2015 GMC Sierra?

P0304 indicates a cylinder 4 misfire, meaning the engine's fourth cylinder is not firing correctly.

2. What are the common symptoms of code P0304 on a 2015 GMC Sierra?

Symptoms include engine roughness, poor fuel economy, lack of power, illuminated check engine light, and possible engine hesitation.

3. What causes a P0304 code on a 2015 GMC Sierra?

Common causes include a faulty spark plug, ignition coil, fuel injector issues, vacuum leaks, low compression, or problems with the cylinder 4 wiring.

4. Can I drive my 2015 GMC Sierra with a P0304 code?

Driving with a P0304 code is not recommended, as prolonged misfires can damage the catalytic converter and other engine components.

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

Start by checking the spark plug, ignition coil, and fuel injector for cylinder 4. Inspect wiring, vacuum hoses, and compression if initial checks don't resolve the issue.

6. How much does it cost to fix a P0304 code on a 2015 GMC Sierra?

Repair costs depend on the cause. Replacing a spark plug or ignition coil may cost $100–$300, while more complex issues like a fuel injector or internal engine repairs can cost significantly more.

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

Yes, a clogged or malfunctioning fuel injector in cylinder 4 can lead to incomplete combustion and trigger the P0304 code.

8. Will replacing the spark plug for cylinder 4 fix a P0304 code?

If the spark plug is the issue, replacing it can resolve the code. However, if the problem persists, further diagnosis is needed.

9. Can low compression in cylinder 4 cause a P0304 code?

Yes, low compression due to worn piston rings, damaged valves, or a blown head gasket can cause a misfire in cylinder 4.

10. How can I prevent a P0304 code on my 2015 GMC Sierra?

Regular maintenance, such as timely spark plug replacements, fuel system cleaning, and checking for vacuum leaks, can help prevent cylinder misfires.

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