P0308
Stop drivingCylinder 8 Misfire Detected
Code P0308 means cylinder 8 is misfiring. Common causes: Ignition coil (40%), spark plug (30%), fuel injector (15%). Drivability: No, stop driving if CEL flashes. Repair cost: $50-$150 DIY, $150-$400 professional.
Can I Drive With P0308?
No, stop driving
Immediate repair needed. If the Check Engine Light is flashing, stop driving to prevent severe damage to your catalytic converter.
Stop driving immediately if: Flashing Check Engine Light, loud engine noises, burning smell, rotten egg smell from exhaust, significant power loss or engine shaking.
Symptoms of P0308
- 1Engine runs rough or shakes
- 2Loss of engine power
- 3Reduced fuel economy
- 4Check Engine Light is on or flashing
- 5Engine hesitation or stumbling
- 6Strong smell of raw fuel from the exhaust
Common Causes of P0308
Parts most likely causing this code, ranked by probability
A faulty ignition coil fails to provide sufficient spark to ignite the fuel-air mixture in cylinder 8.
40% of P0308 cases are fixed by replacing the ignition coil
A worn, fouled, or damaged spark plug in cylinder 8 cannot create a strong enough spark for proper combustion.
30% of P0308 cases are fixed by replacing the spark plug
A clogged or faulty fuel injector in cylinder 8 prevents the correct amount of fuel from reaching the cylinder.
15% of P0308 cases are fixed by replacing the fuel injector
Damaged wiring or a loose connector to the ignition coil or fuel injector for cylinder 8 disrupts electrical signals.
8% of P0308 cases are fixed by repairing wiring or connectors
Low compression in cylinder 8, caused by issues like worn piston rings or a faulty valve, prevents proper combustion.
5% of P0308 cases are fixed by addressing engine compression issues
A vacuum leak near cylinder 8 can lean out the air-fuel mixture, causing a misfire.
2% of P0308 cases are fixed by repairing a vacuum leak
Check These First (Before Buying Parts)
- Listen for the specific sound of a misfire (rough idle, engine shaking).
- Visually inspect the ignition coil and spark plug wire (if applicable) for cylinder 8 for any obvious damage, cracks, or loose connections.
- Check the condition of the spark plug for cylinder 8 if easily accessible.
How to Diagnose P0308
- 1Check if the Check Engine Light is flashing. If it is, stop driving immediately.
- 2Visually inspect the ignition coil and spark plug for cylinder 8 for any obvious damage or loose connections.
- 3Swap the ignition coil from cylinder 8 with a coil from a different cylinder (e.g., cylinder 7). If the misfire moves to the new cylinder, replace the ignition coil.
- 4If the misfire does not move, remove and inspect the spark plug from cylinder 8. Look for fouling, damage, or incorrect gap. Replace if necessary.
- 5If the misfire persists, swap the fuel injector from cylinder 8 with an injector from another cylinder. If the misfire moves, replace the fuel injector.
- 6Perform a compression test on cylinder 8 to check for internal engine problems.
- 7Check wiring and connectors for cylinder 8's ignition coil and fuel injector for continuity and proper connection.
P0308 on Popular Vehicles
Ford F-150
2004-2014P0308 on these F-150s is very common due to ignition coil failure or spark plug issues, particularly on the 5.4L Triton engines. The spark plugs can also be difficult to remove without breaking.
75% fixed by replacing ignition coil or spark plug
Chevrolet Silverado
2007-2013Silverados with the 5.3L V8 engine frequently experience P0308 due to ignition coil failure or fouled spark plugs. Less common but possible are issues with the Active Fuel Management (AFM) lifters causing compression problems.
70% fixed by replacing ignition coil or spark plug
Dodge Ram 1500
2009-2018P0308 on Ram 1500s with the 5.7L Hemi engine is often attributed to ignition coil or spark plug failure. These engines also have a Multi-Displacement System (MDS) that can sometimes lead to misfires if lifters or solenoids fail, though less common for a single cylinder.
70% fixed by replacing ignition coil or spark plug
Frequently Asked Questions
What does P0308 mean?
P0308 indicates that your vehicle's engine computer has detected a misfire in cylinder number 8. This means cylinder 8 is not contributing power to the engine as it should.
Can I drive with P0308?
No, stop driving if your Check Engine Light is flashing. A flashing light means severe misfires are occurring, which can rapidly damage your catalytic converter. If the light is solid, limit driving to essential, short trips and fix it within a few days to prevent further damage.
Will P0308 clear itself?
No, P0308 will not clear itself. A misfire indicates a mechanical or electrical fault that requires diagnosis and repair. The code will remain until the underlying issue is fixed and the system monitors complete their cycles without detecting a misfire.
How do I fix P0308 myself?
Start by checking the spark plug and ignition coil for cylinder 8. You can swap the coil with another cylinder to see if the misfire moves. If not, inspect or replace the spark plug. If the issue persists, you may need to check the fuel injector or perform a compression test.
How much does it cost to fix P0308?
DIY repair costs for P0308 typically range from $50 to $150 for parts like a spark plug or ignition coil. Professional shop repairs usually cost between $150 and $400, depending on the part needing replacement and labor rates.
P0308 keeps coming back - why?
P0308 keeps coming back because the root cause was not fully addressed. This often happens if you only replaced the spark plug when the ignition coil was also failing, or if there's an underlying issue like a faulty fuel injector, wiring problem, or low engine compression that was overlooked.
Will P0308 fail emissions/smog test?
Yes, P0308 will cause your vehicle to fail an emissions or smog test. Misfires increase hydrocarbon emissions significantly, and the Check Engine Light being on (or flashing) is an automatic failure in most inspection programs.
What's the difference between P0308 and P0300?
P0308 specifically indicates a misfire in cylinder #8. P0300, on the other hand, signifies a 'Random/Multiple Cylinder Misfire Detected,' meaning the misfires are not isolated to a single cylinder or are occurring across multiple cylinders without a specific pattern.
P0308 on Ford F-150?
P0308 on a Ford F-150, especially models with the Triton engine, is often caused by a failing ignition coil or a worn spark plug. These engines are known for coil-on-plug designs where individual coils can fail, leading to specific cylinder misfires. Always check the coil and spark plug first.
Questions to Ask Your Mechanic
Did you perform a compression test on cylinder 8?
Good answer: Yes, compression on cylinder 8 is X PSI, which is within specification compared to other cylinders. This rules out internal engine damage.
Did you swap the ignition coil and fuel injector for cylinder 8 to confirm the fault moved?
Good answer: Yes, we swapped the coil and the misfire stayed on cylinder 8, then we swapped the injector and the misfire still stayed on cylinder 8. This confirms the issue is not the coil or injector itself.
Repair Cost Estimate
DIY Repair
Parts only
$50-$150
Shop Repair
Parts + labor
$150-$400
Save $100-$250 by doing it yourself
Difficulty
intermediate
Time
1-3 hours
Intermediate - requires basic mechanical knowledge, specific tools like a spark plug socket, and careful diagnostic steps to avoid replacing unnecessary parts.
Cost of Waiting
Continued misfires send unburned fuel into your exhaust, rapidly overheating and destroying your catalytic converter. A $50-$150 spark plug or ignition coil job now prevents a $800-$2,500 catalytic converter replacement later.
While You're In There...
If your vehicle uses spark plug wires, they often wear out at a similar rate to spark plugs and coils. Replacing them during the same repair prevents future misfires and saves on labor.
Applying dielectric grease to the spark plug boot and ignition coil connection helps prevent corrosion, ensures a good electrical connection, and makes future removal easier.
Applying a small amount of anti-seize to the spark plug threads prevents them from seizing in the cylinder head, making future spark plug changes much easier.
Tools You'll Need
- OBD-II Scan Tool
- Socket Wrench Set
- Spark Plug Socket (specific size for your vehicle)
- Torque Wrench
- Dielectric Grease
- Spark Plug Gap Tool (if applicable)
- Multimeter (for wiring checks)
P0308 is a very common engine code. Most repairs are straightforward, often involving a simple spark plug or ignition coil replacement, and your engine will run smoothly afterward.
- Family-owned since 1957
- 990,000+ happy customers
- Fast nationwide shipping
- Easy returns
Your Next Steps
Step 1: Use an OBD-II scan tool to confirm P0308 is the only misfire code. Clear the code and see if it returns immediately.
Step 2: If the code returns, swap the ignition coil from cylinder 8 with a known good cylinder. If the misfire code changes to the new cylinder, replace the ignition coil for cylinder 8.
Step 3: If the misfire does not move, replace the spark plug for cylinder 8. If the issue persists, consider swapping the fuel injector for cylinder 8 with another cylinder to diagnose further.