AutoCodes – Buick – P0304 Buick

P0304 Buick Code - Cylinder 4 Misfire Detected

Quick Answer

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. Common causes include Faulty Spark Plug #4, Clogged or faulty Fuel Injector #4, Faulty Ignition Coil #4. 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 Buick indicates Cylinder 4 Misfire Detected.
Common causes: Common causes include Faulty Spark Plug #4, Clogged or faulty Fuel Injector #4, Faulty Ignition Coil #4.
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 29,109

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 Aug 09, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0304 Buick 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 P0304 Buick - Cylinder 4 Misfire Detected - AutoCodes.com — P0304 Buick Code - Cylinder 4 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0304 Buick?

Faulty Spark Plug #4
Clogged or faulty Fuel Injector #4
Faulty Ignition Coil #4
Fuel Injector #4 harness is open or shorted
Fuel Injector #4 circuit poor electrical connection
Ignition Coil #4 harness is open or shorted
Ignition Coil #4 circuit poor electrical connection
Insufficient cylinder 4 compression
Incorrect fuel pressure
Intake air leak

How to Fix the DTC P0304 Buick?

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 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 Buick Models:
2000-2020 Buick 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.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0304 Buick 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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Need Help with the Code?

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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 Buick Code

1. What does the OBDII code P0304 mean on a Buick?

P0304 indicates that the engine control module (ECM) has detected a misfire in cylinder 4 of your Buickâ€™s engine.

2. What are the common symptoms of a P0304 code in a Buick?

Symptoms may include rough idling, reduced engine performance, poor fuel economy, the check engine light turning on, and noticeable engine vibrations.

3. What causes a P0304 code in a Buick?

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

4. Can you drive a Buick with a P0304 code?

While it is possible to drive short distances, driving with a P0304 code can lead to further engine damage and should be addressed as soon as possible.

5. How do you fix a P0304 code on a Buick?

Repairs may involve replacing the spark plug or ignition coil for cylinder 4, cleaning or replacing the fuel injector, repairing vacuum leaks, or addressing engine compression issues.

6. How can you diagnose a P0304 code in a Buick?

Diagnosis typically includes checking the spark plug, ignition coil, and fuel injector for cylinder 4, performing a compression test, inspecting for vacuum leaks, and using a scan tool to analyze live data.

7. Is a P0304 code serious for a Buick?

Yes, a P0304 code can cause engine damage if left unresolved, as it may result in unburned fuel damaging the catalytic converter or other engine components.

8. Can bad fuel cause a P0304 code in a Buick?

Yes, contaminated or poor-quality fuel can cause misfires, including a P0304 code, by affecting the fuel injector or combustion process.

9. What tools are needed to troubleshoot a P0304 code in a Buick?

Tools may include a scan tool or OBDII reader, spark plug tester, multimeter, fuel pressure gauge, and a compression tester.

10. How much does it cost to fix a P0304 code on a Buick?

The cost varies depending on the issue but may range from $100 for a spark plug replacement to $500 or more for more extensive repairs like addressing low compression.