Cylinder 4 Misfire Detected
What it means
P0304 means the engine's misfire monitor has detected that cylinder 4 specifically is not firing reliably — fuel isn't burning properly in that cylinder, so the engine runs rough and loses power. Because it's isolated to one cylinder, it usually points to that cylinder's spark plug, coil, or injector. Sustained misfires can overheat and ruin the catalytic converter.
Can I keep driving? Limit driving — a misfire on cylinder 4 dumps raw fuel into the exhaust and can overheat the catalytic converter, especially if the light is flashing.
Real-world scan data
Appears alongside · share of P0304 scans
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
Common symptoms
What you'll notice
- Check-engine light on (flashing during an active misfire)
- Rough idle and noticeable shaking or vibration
- Reduced power and hesitation on acceleration
- Increased fuel consumption and a possible fuel smell
Common causes
Most likely first
- Worn or fouled spark plug on cylinder 4Likely
- Failing ignition coil on cylinder 4Common
- Clogged or leaking fuel injector on cylinder 4Common
- Vacuum leak near cylinder 4's intake runnerLess often
- Low compression on cylinder 4 (valve, ring, or head-gasket issue)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data, then swap the cylinder-4 coil and plug with a neighbouring cylinder and re-scan — if the misfire follows the part, you've found it.
- Inspect and replace the spark plug and coil on cylinder 4 first — the most common cause.
- Test the cylinder-4 injector (resistance and spray) and check fuel delivery.
- Check for a vacuum leak around that runner with carb cleaner or smoke.
- If it persists, run a compression/leak-down test on cylinder 4 for mechanical faults, then clear and re-test.
P0304 by make
Based on commonly reported failure patterns across owner and repair communities, not on our scan data.
BMW
On BMWs, failing ignition coils and worn spark plugs are a common reason for a misfire on cylinder 4, particularly on turbocharged engines. Replace plugs and check the coils together.
Chevrolet
On Chevrolet V8 trucks and SUVs with Active Fuel Management, cylinders 1, 4, 6 and 7 are the ones that shut off to save fuel, and worn lifters on those cylinders are a commonly reported cause of misfires. A ticking noise along with this code is worth getting checked soon.
Dodge
On Dodge cars and SUVs with the 5.7L Hemi and cylinder-deactivation, cylinders 1, 4, 6 and 7 are the ones that shut off, and worn lifters on those cylinders are a commonly reported cause of misfires. A ticking noise along with this code is worth getting checked soon.
Ford
On Ford engines with coil-on-plug ignition, such as the 5.4L Triton, a failing coil or worn spark plug on cylinder 4 is a commonly reported cause. Swapping the coil with a neighbouring cylinder is an easy way to see if the misfire follows it.
GMC
On GMC V8 trucks and SUVs with Active Fuel Management, cylinders 1, 4, 6 and 7 are the ones that shut off to save fuel, and worn lifters on those cylinders are a commonly reported cause of misfires. A ticking noise along with this code is worth getting checked soon.
Honda
On Hondas, a worn plug or coil on cylinder 4 is common, and on V6 models with cylinder deactivation, fouled plugs from oil can also play a part. Check the plug condition before swapping parts.
Hyundai
On Hyundai models, a misfire on cylinder 4 can be a simple coil or plug problem, but on 2.4L four-cylinder engines it can also be a sign of internal engine wear. Get it checked soon if there is knocking or oil use.
Jeep
On Jeeps with the 5.7L Hemi and cylinder-deactivation, cylinders 1, 4, 6 and 7 are the ones that shut off, and worn lifters on those cylinders are a commonly reported cause of misfires. A ticking noise along with this code is worth getting checked soon.
Kia
On Kia models, a misfire on cylinder 4 can be a simple coil or plug problem, but on 2.4L four-cylinder engines it can also be a sign of internal engine wear. Get it checked soon if there is knocking or oil use.
Nissan
On Nissans, ignition coils and spark plugs on cylinder 4 are the usual culprits, particularly on V6 models. Swap coils between cylinders to see if the misfire follows.
Ram
On Ram trucks with the 5.7L Hemi and cylinder-deactivation, cylinders 1, 4, 6 and 7 are the ones that shut off, and worn lifters on those cylinders are a commonly reported cause of misfires. A ticking noise along with this code is worth getting checked soon.
Subaru
On Subarus, plugs and coils on cylinder 4 are the first things to check. On older 2.5L boxer engines, a head gasket leak into a cylinder can also cause misfires.
Toyota
On Toyotas, a failed ignition coil or worn spark plug on cylinder 4 is the usual cause. Swapping the coil with a neighbouring cylinder shows quickly whether the misfire moves.
Volkswagen
On VW and Audi turbo engines, a failing ignition coil on cylinder 4 is a very common cause. Swapping coils between cylinders is a cheap way to confirm it.
FAQ
Quick answers
Is it safe to drive with P0304?+
Can I just clear P0304?+
Related codes
Read & clear P0304 yourself
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