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Engine-Codes – GMC – P0304 2018 GMC Sierra

P0304 2018 GMC Sierra Code - Cylinder 4 Misfire Detected

Quick Answer

The OBD-II code P0304 indicates that a misfire has been detected in cylinder 4 of the engine in a 2018 GMC Sierra. Common causes include Faulty spark plug: A worn-out or damaged spark plug can cause a misfire in the cylinder, Ignition coil failure: A malfunctioning ignition coil can lead to inconsistent spark delivery, Fuel injector issues: A clogged or malfunctioning fuel injector may not deliver fuel properly to the cylinder. 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 2018 GMC Sierra indicates Cylinder 4 Misfire Detected.
Common causes
Common causes include Faulty spark plug: A worn-out or damaged spark plug can cause a misfire in the cylinder, Ignition coil failure: A malfunctioning ignition coil can lead to inconsistent spark delivery, Fuel injector issues: A clogged or malfunctioning fuel injector may not deliver fuel properly to the cylinder.
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 Sep 11, 2024
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Code P0304 2018 GMC Sierra Description

The OBD-II code P0304 indicates that a misfire has been detected in cylinder 4 of the engine in a 2018 GMC Sierra. A misfire occurs when there is a lack of combustion in the cylinder, which can lead to a rough idle, decreased power, and increased emissions. This issue can cause the vehicle to run poorly, leading to reduced fuel efficiency and potential damage to the catalytic converter over time.

OBDII Code P0304 2018 GMC Sierra - Cylinder 4 Misfire Detected
P0304 2018 GMC Sierra Code - Cylinder 4 Misfire Detected

Common Causes of P0304 2018 GMC Sierra

  1. Faulty spark plug: A worn-out or damaged spark plug can cause a misfire in the cylinder.
  2. Ignition coil failure: A malfunctioning ignition coil can lead to inconsistent spark delivery.
  3. Fuel injector issues: A clogged or malfunctioning fuel injector may not deliver fuel properly to the cylinder.
  4. Vacuum leaks: Any leaks in the engine's vacuum system can affect the air-fuel ratio and cause misfires.
  5. Low compression: If there is low compression in the cylinder, combustion may be incomplete, leading to a misfire.

Symptoms of P0304 2018 GMC Sierra

  1. Rough idle: The engine may run unevenly or shake at idle.
  2. Loss of power: The vehicle may feel sluggish or have reduced acceleration.
  3. Increased fuel consumption: Misfires can lead to inefficient combustion, resulting in poor fuel economy.
  4. Engine vibration: A misfiring cylinder can cause the engine to vibrate more than usual.
  5. Check Engine Light: The Check Engine Light may illuminate on the dashboard, indicating a problem with the engine.

How to Fix P0304 2018 GMC Sierra

  1. Diagnose the issue: Use a scan tool to identify which cylinder is misfiring and check for any related trouble codes.
  2. Inspect spark plugs and ignition coils: Check the condition of the spark plug in cylinder 4 and inspect the ignition coil for any signs of damage.
  3. Test fuel injector: Perform a fuel injector test to ensure proper fuel delivery to the cylinder.
  4. Check compression: Measure the compression in cylinder 4 to determine if there are any mechanical issues.
  5. Replace faulty components: Replace any faulty spark plugs, ignition coils, fuel injectors, or repair any vacuum leaks to resolve the misfire.

Cost to Fix P0304 2018 GMC Sierra

The cost of repairing a cylinder 4 misfire in a 2018 GMC Sierra can vary depending on the specific cause of the issue and the parts needed for the repair. On average, the cost of parts such as spark plugs, ignition coils, or fuel injectors can range from $50 to $200 per component. Labor costs at auto repair shops typically range from $80 to $150 per hour, with the total repair cost potentially totaling a few hundred dollars. It's important to factor in diagnostic time and any additional repairs that may be needed to address the underlying cause of the misfire.

What does this mean?

Tech Notes for P0304 2018 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 2018 GMC Sierra code?

Need more information on how to fix the P0304 2018 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 2018 GMC Sierra Code

1. What does the OBDII code P0304 mean on a 2018 GMC Sierra?

P0304 indicates that the engine control module (ECM) has detected a misfire specifically in cylinder 4.

2. What are common symptoms of the P0304 code in a 2018 GMC Sierra?

Symptoms may include a rough idle, reduced engine performance, poor fuel economy, illuminated check engine light, and in severe cases, engine stalling or hesitation.

3. What can cause a P0304 code on a 2018 GMC Sierra?

Common causes include a faulty spark plug or ignition coil in cylinder 4, a clogged fuel injector, low engine compression, vacuum leaks, or issues with the ECM.

4. Can driving with a P0304 code damage my 2018 GMC Sierra?

Yes, driving with a misfire can cause further engine damage, such as overheating the catalytic converter or damaging other engine components.

5. How can I diagnose the P0304 code on my 2018 GMC Sierra?

Diagnosis involves checking cylinder 4's spark plug, ignition coil, and fuel injector, as well as performing a compression test and inspecting for vacuum leaks.

6. How do I fix the P0304 code on a 2018 GMC Sierra?

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

7. Can a dirty air filter cause the P0304 code on a 2018 GMC Sierra?

While a dirty air filter can impact overall engine performance, it is unlikely to specifically cause a cylinder 4 misfire.

8. How much does it cost to repair a P0304 code on a 2018 GMC Sierra?

The cost varies depending on the cause. Replacing a spark plug or ignition coil can cost $50–$300, while addressing more complex issues like low compression can be significantly more expensive.

9. Will resetting the check engine light fix the P0304 code on a 2018 GMC Sierra?

Resetting the light without addressing the root cause will not fix the misfire, and the code is likely to return.

10. Can bad fuel cause a P0304 code on a 2018 GMC Sierra?

Yes, bad or contaminated fuel can lead to misfires, including in cylinder 4, by causing improper combustion.

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