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Engine-Codes – GMC – P0305 GMC

P0305 GMC Code - Cylinder 5 Misfire Detected

Quick Answer

When a GMC vehicle displays diagnostic code P0305, it indicates that a misfire has been detected in cylinder 5 of the engine. Common causes include Faulty spark plug in cylinder 5, Malfunctioning ignition coil, Clogged fuel injector in cylinder 5. 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
P0305 GMC indicates Cylinder 5 Misfire Detected.
Common causes
Common causes include Faulty spark plug in cylinder 5, Malfunctioning ignition coil, Clogged fuel injector in cylinder 5.
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 25, 2024
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Code P0305 GMC Description

When a GMC vehicle displays diagnostic code P0305, it indicates that a misfire has been detected in cylinder 5 of the engine. A misfire occurs when the fuel in the combustion chamber fails to ignite at the right time or does not ignite at all. This can lead to a lack of power, rough idling, poor fuel efficiency, and potential damage to the catalytic converter over time.

OBDII Code P0305 GMC - Cylinder 5 Misfire Detected
P0305 GMC Code - Cylinder 5 Misfire Detected

Common Causes of P0305 GMC

  1. Faulty spark plug in cylinder 5
  2. Malfunctioning ignition coil
  3. Clogged fuel injector in cylinder 5
  4. Low compression in cylinder 5
  5. Vacuum leak affecting cylinder 5

Symptoms of P0305 GMC

  1. Rough idling or shaking while the vehicle is at a standstill
  2. Loss of power or hesitation during acceleration
  3. Increased fuel consumption
  4. Engine knocking or pinging sounds
  5. Check Engine Light illuminated on the dashboard

How to Fix P0305 GMC

  1. Diagnose the specific cause of the misfire in cylinder 5 using a scan tool
  2. Replace the spark plug in cylinder 5 if it is found to be faulty
  3. Test and potentially replace the ignition coil for cylinder 5
  4. Clean or replace the fuel injector in cylinder 5 if it is clogged
  5. Perform a compression test on cylinder 5 to check for any issues and address as necessary

Cost to Fix P0305 GMC

The cost of repairing a cylinder 5 misfire in a GMC vehicle can vary depending on the underlying cause of the issue. Typical repair costs for this type of problem can range from $100 to $500, including parts and labor. It's important to keep in mind that the final cost may be higher or lower based on the specific diagnosis time and labor rates at the auto repair shop, as well as the vehicle's make and model. Be sure to inquire about the rates in your local area for a more accurate estimate.

What does this mean?

Tech Notes for P0305 GMC

The P0305 code means that the cylinder 5 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 5. 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 GMC Models:
2000-2020 GMC Factory Service Bulletin OBDII Code P0305
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 P0305 GMC code?

Need more information on how to fix the P0305 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0305 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

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 P0305 GMC Code

1. What does the P0305 code mean on a GMC?

The P0305 code indicates a misfire has been detected in cylinder 5 of the engine.

2. What are the common symptoms of a P0305 code?

Symptoms may include rough idle, reduced engine performance, poor fuel economy, hesitation during acceleration, and the Check Engine Light turning on.

3. What can cause a cylinder 5 misfire in a GMC?

Common causes include a faulty spark plug, a bad ignition coil, a clogged fuel injector, low cylinder compression, or a vacuum leak near cylinder 5.

4. Can I drive my GMC with a P0305 code?

Driving with a P0305 code is not recommended as it can lead to further engine damage or catalytic converter failure if the misfire persists.

5. How do I fix the P0305 code on my GMC?

Repairs may involve replacing the spark plug or ignition coil for cylinder 5, cleaning or replacing the fuel injector, addressing vacuum leaks, or performing a compression test to check for internal engine issues.

6. How much does it cost to fix a P0305 code?

Costs vary depending on the cause. Replacing a spark plug or ignition coil may cost $100–$300, while more extensive repairs like fixing compression issues could cost significantly more.

7. Can a dirty air filter cause a P0305 code?

While unlikely, a severely clogged air filter can contribute to misfire issues by affecting the air-fuel mixture, but it’s not a common cause specific to cylinder 5.

8. How can I diagnose a P0305 code on my GMC?

Diagnosis typically involves using an OBDII scanner, inspecting the spark plug and ignition coil for cylinder 5, checking the fuel injector, and testing for vacuum leaks or low compression.

9. Can bad fuel cause a P0305 code?

Yes, contaminated or low-quality fuel can cause misfires, including in cylinder 5, by disrupting proper combustion.

10. Will clearing the P0305 code fix the problem?

Clearing the code will turn off the Check Engine Light temporarily, but the underlying issue causing the misfire must be resolved to prevent the code from returning.

Discuss the causes and fixes for P0305 GMC OBDII Code

Submit a New Comment

  • Please include spark plug wire as second in possible causes. I had this code, spark plug was good but the wire was not. Checked resistance on No 5 wire and there was none so I replace all spark plug wires, and the code clear, problem solved.

    Reply to Comment

  • Done. Thanks for the information!!

    Reply to Comment