AutoCodes – GMC – P0303 2017 GMC Sierra

P0303 2017 GMC Sierra Code - Cylinder 3 Misfire Detected

Quick Answer

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. Common causes include Faulty Spark Plug #3, Clogged or faulty Fuel Injector #3, Faulty Ignition Coil #3. 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 2017 GMC Sierra indicates Cylinder 3 Misfire Detected.
Common causes: Common causes include Faulty Spark Plug #3, Clogged or faulty Fuel Injector #3, Faulty Ignition Coil #3.
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 335

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 Jul 23, 2023

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0303 2017 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 P0303 2017 GMC Sierra - Cylinder 3 Misfire Detected - AutoCodes.com — P0303 2017 GMC Sierra Code - Cylinder 3 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0303 2017 GMC Sierra?

Faulty Spark Plug #3
Clogged or faulty Fuel Injector #3
Faulty Ignition Coil #3
Fuel Injector #3 harness is open or shorted
Fuel Injector #3 circuit poor electrical connection
Ignition Coil #3 harness is open or shorted
Ignition Coil #3 circuit poor electrical connection
Insufficient cylinder 3 compression
Incorrect fuel pressure
Intake air leak

How to Fix the DTC P0303 2017 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 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.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0303 2017 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 P0303 2017 GMC Sierra Code

What does OBDII code P0303 mean for a 2017 GMC Sierra?

P0303 indicates a misfire has been detected in cylinder 3 of the engine.

What are the common symptoms of code P0303 in a 2017 GMC Sierra?

Symptoms may include rough idling, reduced engine power, poor fuel efficiency, and the Check Engine Light illuminated.

What causes code P0303 in a 2017 GMC Sierra?

Common causes include a faulty spark plug, a malfunctioning ignition coil, a clogged fuel injector, low cylinder compression, or vacuum leaks near cylinder 3.

Can driving with code P0303 damage my 2017 GMC Sierra?

Yes, prolonged driving with a misfire can cause damage to the catalytic converter and other engine components.

How can I diagnose code P0303 in a 2017 GMC Sierra?

Start by inspecting the spark plug, ignition coil, and fuel injector for cylinder 3. You may also need to perform a compression test or check for vacuum leaks.

How do I fix code P0303 on a 2017 GMC Sierra?

Repairs may include replacing the spark plug or ignition coil for cylinder 3, cleaning or replacing the fuel injector, or addressing any mechanical issues like compression problems.

Is replacing the spark plug enough to fix code P0303 in a 2017 GMC Sierra?

Replacing the spark plug may resolve the issue if the misfire is caused by a worn or faulty plug, but other components like the ignition coil or fuel injector may also need attention.

Can bad fuel cause code P0303 in a 2017 GMC Sierra?

Yes, low-quality or contaminated fuel can lead to misfires, including in cylinder 3.

How much does it cost to repair code P0303 on a 2017 GMC Sierra?

Repair costs can vary widely, from $50 for a spark plug replacement to several hundred dollars for more complex fixes like addressing a fuel injector or compression issue.

Can a dirty air filter trigger code P0303 in a 2017 GMC Sierra?

A dirty air filter is unlikely to directly cause this code but can contribute to overall engine performance issues that may exacerbate a misfire.