AutoCodes – Hummer – P0304 Hummer

P0304 Hummer 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 Hummer 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 8,792

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 Jun 13, 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 Hummer 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 Hummer - Cylinder 4 Misfire Detected - AutoCodes.com — P0304 Hummer Code - Cylinder 4 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0304 Hummer?

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 Hummer?

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".

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0304 Hummer 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 P0304 Hummer Code

1. What are the common symptoms of OBDII code P0304 in a Hummer?

- Common symptoms include rough idling, engine misfiring, loss of power, and potentially increased fuel consumption.

2. What are the typical causes of a cylinder 4 misfire detected in a Hummer?

- Potential causes include faulty spark plugs, ignition coil issues, vacuum leaks, fuel delivery problems, or a malfunctioning fuel injector.

3. How can I diagnose the source of the cylinder 4 misfire in my Hummer?

- Diagnose by checking spark plugs, ignition coils, fuel injectors, vacuum leaks, and performing a compression test to pinpoint the exact cause.

4. Can driving with a cylinder 4 misfire in a Hummer cause further damage?

- Yes, driving with a misfiring cylinder can lead to damage to the catalytic converter, oxygen sensors, and other engine components over time.

5. How can I repair a cylinder 4 misfire in my Hummer?

- Repair steps may include replacing spark plugs, ignition coils, fuel injectors, fixing vacuum leaks, or addressing any other issues identified during diagnosis.

6. Is it safe to continue driving my Hummer with OBDII code P0304?

- It is not recommended to drive with a cylinder 4 misfire as it can cause damage to the engine and other components. It's best to address the issue promptly.

7. Can a dirty fuel filter cause a cylinder 4 misfire in a Hummer?

- Yes, a dirty fuel filter can restrict fuel flow to the cylinder, leading to a misfire. It's important to check and replace a clogged fuel filter if needed.

8. Will resetting the OBDII code P0304 in my Hummer make the issue go away?

- Simply clearing the code without addressing the underlying cause will not fix the misfire problem. It's essential to diagnose and repair the issue for a lasting solution.

9. Are there any maintenance tips to prevent cylinder misfires in a Hummer?

- Regular maintenance such as changing spark plugs, inspecting ignition components, and ensuring proper fuel system operation can help prevent cylinder misfires.

10. How much does it typically cost to repair a cylinder 4 misfire in a Hummer?

- The cost of repairs can vary depending on the exact cause of the misfire, but it may range from a few hundred to over a thousand dollars, including parts and labor.