AutoCodes – Honda – P0304 Honda

P0304 Honda Code - No. 4 Cylinder Misfire Detected

Quick Answer

The crankshaft vibrates slightly when each cylinder fires. Common causes include Valve adjustment, Faulty spark plug #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 Honda indicates No. 4 Cylinder Misfire Detected.
Common causes: Common causes include Valve adjustment, Faulty spark plug #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 85,603

How popular is this code, among other codes? Medium

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 16, 2023

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0304 Honda Description

The crankshaft vibrates slightly when each cylinder fires. If a misfire occurs, the crankshaft rotation speed changes rapidly. The Powertrain Control Module (PCM) monitors the crankshaft rotation speed based on the output pulses from the Crankshaft Position (CKP) Sensor. By monitoring changes in the crankshaft rotation speed, the PCM counts the number of misfires and determines which cylinder is misfiring. If a misfire is detected, a Diagnostic Trouble Code (DTC) is stored.
There are two types of misfire detection: Type 1: When the number of misfires per 200 engine revolutions reaches the level that can damage the three-way catalyst (TWC), a DTC is stored and the MIL blinks. Type 2: When the number of misfires per 1,000 engine revolutions reaches the level that affects exhaust emissions but is not severe enough to immediately damage the catalyst, a DTC is stored, and the MIL comes on.

OBDII Code P0304 Honda - No. 4 Cylinder Misfire Detected - AutoCodes.com — P0304 Honda Code - No. 4 Cylinder Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0304 Honda?

Valve adjustment
Faulty spark plug #4
Faulty ignition coil #4
Clogged or faulty fuel injector #4
Intake air leak
Insufficient cylinder #4 compression
Incorrect fuel pressure

How to Fix the DTC P0304 Honda?

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 Honda 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.

Need more information about the P0304 Honda code?

Need more information on how to fix the P0304 Honda code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0304 Honda code diagnosed by a professional: Find a repair shop in your area

Information for Specific Honda Models

P0304 2008 Honda Accord — Cylinder Number 4 Misfire Detected
P0304 2009 Honda Accord — Cylinder Number 4 Misfire Detected
P0304 2010 Honda Accord — Cylinder Number 4 Misfire Detected
P0304 1996 Honda Civic — Cylinder Number 4 Misfire Detected
P0304 1997 Honda Civic — Cylinder Number 4 Misfire Detected
P0304 1998 Honda Civic — Cylinder Number 4 Misfire Detected
P0304 1999 Honda Civic — Cylinder Number 4 Misfire Detected
P0304 2000 Honda Civic — Cylinder Number 4 Misfire Detected
P0304 2016 Honda CR-V — No. 4 Cylinder Misfire Detected
P0304 2017 Honda CR-V — No. 4 Cylinder Misfire Detected
P0304 2018 Honda CR-V — No. 4 Cylinder Misfire Detected
P0304 2019 Honda CR-V — No. 4 Cylinder Misfire Detected
P0304 2020 Honda CR-V — No. 4 Cylinder Misfire Detected
P0304 2021 Honda CR-V — No. 4 Cylinder Misfire Detected

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 Honda Code

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

Symptoms include engine misfire, loss of power, rough idling, and potential engine vibration.

2. What are the typical causes of a No. 4 cylinder misfire detected in a Honda?

Common causes include faulty spark plugs, ignition coils, fuel injectors, vacuum leaks, or low compression in the No. 4 cylinder.

3. How can I diagnose the source of the misfire in the No. 4 cylinder of my Honda?

You can diagnose the issue by performing a visual inspection of spark plugs, checking ignition coils, testing fuel injectors, and conducting a compression test on the affected cylinder.

4. Can driving with a P0304 code harm my Honda's engine?

Continued driving with a misfire can potentially damage the catalytic converter and other engine components, so it's advisable to address the issue promptly.

5. Are there any simple fixes I can try before taking my Honda to a mechanic for a P0304 code?

You can start by checking and replacing the spark plugs, inspecting the ignition coil for damage, and ensuring there are no vacuum leaks around the No. 4 cylinder.

6. How much does it typically cost to repair a No. 4 cylinder misfire in a Honda?

The cost can vary depending on the exact cause of the misfire, but it may range from $100 to $500 for parts and labor.

7. Can a dirty fuel system cause a No. 4 cylinder misfire in a Honda triggering code P0304?

Yes, a dirty fuel system can lead to poor fuel delivery to the No. 4 cylinder, causing a misfire and triggering the P0304 code.

8. Is it safe to continue driving my Honda if the check engine light is on due to code P0304?

It is not recommended to drive the vehicle extensively with a misfire issue as it can lead to further damage and potentially unsafe driving conditions.

9. Can extreme weather conditions affect the occurrence of a No. 4 cylinder misfire in a Honda?

Yes, extreme temperatures or humidity levels can impact the ignition system and fuel delivery, potentially leading to a misfire in the No. 4 cylinder.

10. How often should I perform maintenance to prevent a No. 4 cylinder misfire in my Honda?

Regular maintenance, including timely spark plug replacements, fuel system cleaning, and periodic checks of ignition components, can help prevent misfire issues in your Honda.

Discuss the causes and fixes for P0304 Honda OBDII Code

Submit a New Comment

rpeha
Date: August 31, 2014 at 12:41 am

rough idle at start up, goes away when engine warms up.

Reply to Comment
OBDIITech
Date: August 31, 2014 at 3:08 am

What model and year is your Honda?

Reply to Comment
dre
Date: October 2, 2014 at 2:36 pm

i have a Honda crv is misfiring in the number four cylinder,once it has heaten up t goes away

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OBDIITech
Date: October 2, 2014 at 5:03 pm

If the spark plugs are OK, you should perform a compression test. May have a blown head gasket.

Reply to Comment
ish
Date: October 6, 2014 at 6:46 pm

I have a 2000 civic ex my compression on the 4th cylinder is about 30 what dou you think it is?

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OBDIITech
Date: October 6, 2014 at 6:56 pm

More than likely a head gasket.

Reply to Comment
Sen
Date: September 29, 2015 at 6:44 pm

P0304 cylinder 4 random misfire. Replaced ignition wires, plugs, dristributor cap and rotor. Ran injector cleaner through engine and still having engine hesitation sometimes. Still reading code p0304. What do I do next swap ingectors?

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OBDIITech
Date: September 29, 2015 at 8:53 pm

What model and year is your Honda? You may have to adjust the valves.

Reply to Comment
Everardo
Date: December 1, 2015 at 5:20 am

Hi, I keep getting the code P0304, P0301,P0303 and random misfire. I have a Honda Odyssey 2006, 3.5. I already replaced the spark plugs and the fuel injectors. What could it be?

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OBDIITech
Date: December 1, 2015 at 11:00 pm

Valve adjustment it's probably the most likely cause of the problem.

Reply to Comment
Julius
Date: April 15, 2016 at 3:04 pm

Driving a Honda Insight from 2012, and this error code was the cause of a complete engine failure due to a faulty (overheated) spark plug. Was driving for an hour on the highway before a rather noticeable pop caused a complete loss of power (automatic car, went to neutral). After cooling down, error disappeared but engine did not run anymore. Just got a call from the mechanics that they had to open up the motor block to assess the damage, since parts of the spark plug seem to have gotten missing...

Reply to Comment
ZIGS
Date: February 3, 2018 at 2:40 pm

MOST RANDOM NOT HARD BMISS FIRE ON MOST HONDAS ARE PLUGS OR VALVE ADJUST MENT. IF YOU LOOK AT (MAP) SENSOR IT SHOULD BE AROUND .88 MUCH HIGER READINGS THE VALES ARE OUT MOST LIKELY. THE EXAUST VALVES GET TIGHT AND HANG OPEN CAUSING THE MISS FIRE.

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