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P0303 2018 GMC Sierra Code - Cylinder 3 Misfire Detected

Quick Answer

When the OBD-II system detects a misfire in cylinder 3 of a 2018 GMC Sierra, it triggers diagnostic trouble code P0303. Common causes include Worn or fouled spark plugs, Faulty ignition coil, Clogged fuel injector. 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
P0303 2018 GMC Sierra indicates Cylinder 3 Misfire Detected.
Common causes
Common causes include Worn or fouled spark plugs, Faulty ignition coil, Clogged fuel injector.
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 12, 2024
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Code P0303 2018 GMC Sierra Description

When the OBD-II system detects a misfire in cylinder 3 of a 2018 GMC Sierra, it triggers diagnostic trouble code P0303. This means that the engine's computer has detected that the cylinder is not firing properly, which can lead to a range of issues affecting the vehicle's performance. A misfire occurs when the air-fuel mixture in the cylinder does not ignite properly, causing a disruption in the combustion process. This can result in power loss, rough idling, decreased fuel efficiency, and increased emissions.

OBDII Code P0303 2018 GMC Sierra - Cylinder 3 Misfire Detected
P0303 2018 GMC Sierra Code - Cylinder 3 Misfire Detected

Common Causes of P0303 2018 GMC Sierra

  1. Worn or fouled spark plugs
  2. Faulty ignition coil
  3. Clogged fuel injector
  4. Vacuum leaks in the intake manifold
  5. Low compression in cylinder 3

Symptoms of P0303 2018 GMC Sierra

  1. Engine misfires or runs rough
  2. Loss of power and acceleration
  3. Increased fuel consumption
  4. Engine vibration or shaking
  5. Illuminated check engine light

How to Fix P0303 2018 GMC Sierra

  1. Diagnose the specific cause of the misfire by performing a thorough inspection of the spark plugs, ignition coil, fuel injector, and compression in cylinder 3.
  2. Replace any faulty spark plugs or ignition coils that are causing the misfire.
  3. Clean or replace clogged fuel injectors to ensure proper fuel delivery to the cylinder.
  4. Check for vacuum leaks in the intake manifold and repair as needed.
  5. Perform a compression test on cylinder 3 to determine if there are any issues with the engine's internal components.

Cost to Fix P0303 2018 GMC Sierra

The cost of repairing a cylinder 3 misfire in a 2018 GMC Sierra can vary depending on the specific cause of the issue and the prices of parts and labor in your area. On average, you can expect to pay between $100 and $300 for parts such as spark plugs, ignition coils, and fuel injectors. Labor costs can range from $100 to $300 or more, depending on the complexity of the repair and the shop's hourly rate. It's recommended to get a detailed estimate from a trusted auto repair shop to get an accurate cost for resolving this issue.

What does this mean?

Tech Notes for P0303 2018 GMC Sierra

The P0303 code means that cylinder 3 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 3. 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 P0303

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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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.

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