P0304 OBD-II Trouble Code: Cylinder 4 Misfire Detected

Our certified mechanics come to you · Get a fair and transparent estimate upfront

Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0304 code

P0304 is a diagnostic trouble code (DTC) for "Cylinder 4 Misfire Detected". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$20.00
Toyota$20.00
BMW$20.00
SCHEDULE P0304 DIAGNOSTIC Get a fair and transparent estimate upfront

P0304 code definition

P0304 is a diagnostic trouble code seen when a misfire is detected in cylinder 4. This code may be seen with other misfire codes and lean / rich codes.

What the P0304 code means

The P0304 code will be seen in cars where the ECU has detected that cylinder 4 is not firing properly. The ECU monitors the operation of all cylinders to ensure they are all firing on time, so when one misfires repeatedly, a Check Engine Light is set.

What causes the P0304 code?

  • Faulty spark plug
  • Faulty plug wires, cap and rotor, and/or coil pack
  • Mechanical engine issue
  • Intake leak
  • Fuel issues

What are the symptoms of the P0304 code?

  • Engine running poorly or having trouble staying running
  • Check Engine Light present
  • Misfires
  • Lack of engine power
  • Decreased fuel mileage

How does a mechanic diagnose the P0304 code?

  • The mechanic will begin by hooking up a scan tool to the DLC port to determine which codes are present.

  • Freeze frame data will be associated with every code found and should be noted for use on the test drive.

  • The codes will now be cleared and a road test performed under similar conditions to the freeze frame data from earlier.

  • Next, a visual inspection will be performed looking for damaged wires, worn or broken components, or visible leaks.

  • Next, the scan tool will be used to monitor the misfire counter for cylinder 4.

  • Then, the scan tool will be used to look at the long-term fuel trims to see if fuel issues are present and the intake air pressure checked to see if vacuum leaks are present.

Common mistakes when diagnosing the P0304 code

Mistakes can be made when components are not tested or when unnecessary components are replaced. To avoid this, follow all steps without skipping any. Replacing the spark plugs and wires fixes this issue for most vehicles. However, the entire system must be tested before determining what to repair.

How serious is the P0304 code?

P0304 should not prevent the vehicle from being driven to a safe location once symptoms start. With the potential for drivability problems associated with this code, it is advised to have it repaired as soon as possible for safe vehicle operation.

What repairs can fix the P0304 code?

Additional comments for consideration regarding the P0304 code

Coil pack equipped vehicles with higher mileage may experience coil pack failure. An easy way to test if the coil itself is at fault is to move the suspect coil pack to another cylinder. Then test drive the vehicle to see if the code changes to the new cylinder. If it does, then the coil pack itself has failed.

Depending on year, vehicles will be equipped with either coil packs which are the most modern, spark plug wires which are a little bit older, or a distributor cap and rotor which is usually on carbureted vehicles. All of these are considered wear items, and are prone to failure on higher mileage vehicles. The spark plug wires and cap and rotor are items that are generally replaced along with spark plugs at routine intervals.

An advanced level scan tool will be needed to properly diagnose P0304 - one that does not just simply read the code, but gives access to live engine data. This data will be needed to track misfires and view both fuel and intake information.

Need help with a P0304 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

trouble codes
P0304
Check Engine Light

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0304 code.

SCHEDULE P0304 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating


YourMechanic Check Engine Light is on Inspection Service

Average Rating

4.8/5

Number of Reviews

4,987

Rating Summary
4,593
191
48
28
127
4,593
191
48
28
127

Robert

12 years of experience
6 reviews
Robert
12 years of experience
Ford Fusion - Check Engine Light is on - Stockton, California
Robert was very knowledgeable and professional. He is also very friendly and likable individual. I’m very pleased and satisfied with his work.

Sonal

16 years of experience
19 reviews
Sonal
16 years of experience
Mercedes-Benz S550 - Check Engine Light is on - Federal Way, Washington
Sonal was very knowledgeable and took the time to explain each of the 50 point checklist thoroughly. Sonal definitely has an abundance of Mercwdes Benz experience regarding mechanical problems.

Daniel

20 years of experience
301 reviews
Daniel
20 years of experience
Chrysler Town & Country - Check Engine Light is on - Santa Fe, Texas
Daniel was on time and performed a 50 inspection for us. We now have a path forward for repair and will be scheduling Daniel to return and make the repairs.

Michael

15 years of experience
515 reviews
Michael
15 years of experience
Chevrolet Equinox - Check Engine Light is on - Woodstock, Georgia
Mike really knows his stuff. He took alot of time with me making sure I understood what was going on with my vehicle.


Related questions

Car misfires when driving 45+ mph for extended period of time

The code P0304 is a misfire on cylinder number four. The reason it is misfiring at cruising speed is that is when the engine is running its leanest and the coil is finding an easier path to ground than through...

Getting error code P0304

P0304 means the engine computer has detected a severe misfire on cylinder 4. This could be due to a bad ignition coil, spark plug, fuel injector, or valve train issue. If the issue is not resolved, further damage to the...

P0304 Misfiring on Cylinder 4

Hello. If the spark plug and the coil have been replaced, then a compression test needs to be done. It is common for the valve seat to fail and cause this. When it fails, it causes low compression which then...

More related articles

P0365 OBD-II Trouble Code: Camshaft Position Sensor B Circuit (Bank 1)
P0365 code definition The P0365 code means that the car’s computer has detected a fault in the camshaft position sensor B in...
P2409 OBD-II Trouble Code: Fuel Cap Sensor/Switch Circuit Range/Performance
P2409 P2409 code definition Fuel Cap Sensor/Switch Circuit Range/Performance What the P2409 code means P2409 is an OBD-II generic code for the Engine Control module (ECM) detecting the fuel cap sensor, switch or circuit is out of range or performance...
What Gases Does the OBD Detect in the Exhaust?
Your Your engine runs on combustion – fire – which creates exhaust gases. A wide range of gases are produced during normal operation, and they must be controlled because many of them become pollutants when released into the atmosphere. It’s...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1-800-701-6230 · hi@yourmechanic.com