P0304 GMC 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 GMC 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.
Code P0304 GMC Description
What are the Possible Causes of the DTC P0304 GMC?
- 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 GMC?
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.
Code Tech Notes
There is a Factory Service Bulletins for All 2000-2020 GMC Models:
2000-2020 GMC 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 GMC 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 GMC code?
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Need Help with the Code?
Get the P0304 GMC code diagnosed by a professional: Find a repair shop in your area
Information for Specific GMC Models
- P0304 2014 GMC Sierra — Cylinder 4 Misfire Detected
- P0304 2015 GMC Sierra — Cylinder 4 Misfire Detected
- P0304 2016 GMC Sierra — Cylinder 4 Misfire Detected
- P0304 2017 GMC Sierra — Cylinder 4 Misfire Detected
- P0304 2018 GMC Sierra — Cylinder 4 Misfire Detected
Frequently Asked Questions about P0304 GMC Code
1. What are the common symptoms of OBDII code P0304 (Cylinder 4 Misfire Detected)?
Symptoms may include rough idling, engine vibration, loss of power, decreased fuel efficiency, and potentially, the illumination of the Check Engine Light.
2. What are some possible causes of OBDII code P0304 (Cylinder 4 Misfire Detected)?
Potential causes include faulty spark plugs, ignition coils, fuel injectors, vacuum leaks, low compression in the cylinder, or issues with the engine's computer system.
3. How can I diagnose the cause of OBDII code P0304 (Cylinder 4 Misfire Detected)?
Diagnosis typically involves inspecting and testing the spark plugs, ignition coils, fuel injectors, compression levels, and checking for vacuum leaks using a scan tool and performing a visual inspection.
4. Can driving with OBDII code P0304 (Cylinder 4 Misfire Detected) cause further damage to the vehicle?
Continuing to drive with a misfire can potentially lead to damage to the catalytic converter, oxygen sensors, or other engine components, so it is advisable to address the issue promptly.
5. What are some repair tips for fixing OBDII code P0304 (Cylinder 4 Misfire Detected)?
Repair tips may include replacing faulty spark plugs, ignition coils, or fuel injectors in cylinder 4, addressing any vacuum leaks, performing a compression test, and ensuring proper engine timing.
6. Is it safe to continue driving with the Check Engine Light on due to OBDII code P0304 (Cylinder 4 Misfire Detected)?
While the vehicle may still be operable, it is recommended to address the issue promptly to prevent potential damage and ensure optimal engine performance.
7. Can a DIY enthusiast fix OBDII code P0304 (Cylinder 4 Misfire Detected) at home?
Depending on the individual's mechanical skills and access to tools, some DIY enthusiasts may be able to address the misfire issue by following repair guides or tutorials specific to their vehicle.
8. How much does it typically cost to repair OBDII code P0304 (Cylinder 4 Misfire Detected) at a mechanic or dealership?
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, considering parts and labor expenses.
9. Are there any preventive measures to avoid OBDII code P0304 (Cylinder 4 Misfire Detected) in the future?
Regular maintenance, such as replacing spark plugs at recommended intervals, using quality fuel, and addressing engine performance issues promptly, can help prevent misfires and related trouble codes.
10. How long does it take to repair OBDII code P0304 (Cylinder 4 Misfire Detected)?
The repair time can vary based on the cause of the misfire and the complexity of the repair, but it may take anywhere from a few hours to a full day, depending on the extent of the issue and the mechanic's workload.
Discuss the causes and fixes for P0304 GMC OBDII Code
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Pls help ,I already change ,cap,rotor ,wires ,spark plugs and double check wires spark plugs conect,replacegas filter,add injectors cleaner and stil on PO304 ,gmc sonoma V6 '02 pls help !
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You could have a problem with a valve. I suggest performing a compression test.
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The problem i am having is this.... When i bought the truck it ran rough. Couple days later the truck decided not to run. I noticed smoke coming from the intake manifold. it melted and smoked real bad. I replaced the intake and gaskets and it ran fine for a couple weeks. Then the CEL starts flashing after 25 MPH. Now the CEL is always on and only flashes above 25 MPH. does not matter if it is hot or cold. I have replaced all plugs wires and coils. I replaced intake gaskets again and bench cleaned injectors. I am at a loss. Any ideas?
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What model and year is your vehicle? have you tried swapping the fuel injectors? besides the P0304 code any other codes?
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Title says 1999 GMC Sierra Lt. But when I buy parts some are required to be 2000 due to the manufacturing date. It has the 4.8 engine. Only other code is p0443 purge valve circuit.
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I would start by swapping the fuel injector. Sounds like the problem is either a bad fuel injector or the fuel injector connector. I checked a national database of of repair for you model and year, and other than the spark plugs, intake gasket, and wires, the fuel injector is the most common problem.
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So I finally had a chance to switch injectors 4 and 8. Code did not move with injector.
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Please Help! 1999 Gmc Jimmy 4.3l v6 misfire cylinder 4, replaced spider, cap and rotor, spark plugs and wires and MAF still failing misfire 4 what can I do??
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Other than the components you have replaced I don't any anything else setting a single cylinder misfire code, but I did find a bulletin with the following information. I hope that helps
If you encounter vehicles that exhibit the above conditions, refer to SI for the appropriate DTC(s) set. If no trouble is found, the cause may be due to an ECM ground terminal that has corroded with rust over time. Inspect the main engine wiring harness ground terminal (G103) for this condition.
The wire terminal attaches either to the front or to the rear of the right side cylinder head, depending on the model year of the Full Size Pickup and/or Utility Trucks. If the ECM ground terminal has been found to be corroded, then follow the service procedure outlined in this bulletin to correct the corrosion issue.
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