P0303
Fix within a few daysYour engine's computer detected that cylinder #3 is misfiring, meaning it's not burning fuel correctly.
Code P0303 means Cylinder 3 Misfire Detected. Common causes: Ignition coil (40%), spark plug (35%), fuel injector (15%). Drivability: Limit driving, fix within a few days. Repair cost: $50-$200 DIY, $150-$500 professional.
Can I Drive With P0303?
Limit driving, fix within a few days
Essential trips under 10 miles, avoid highways and heavy acceleration. If the Check Engine Light is flashing, stop driving immediately.
Stop driving immediately if: Flashing CEL, loud knocking noises, burning smell, rotten egg smell from exhaust, significant power loss
Symptoms of P0303
- 1Engine running rough or shaking
- 2Loss of engine power
- 3Poor acceleration
- 4Reduced fuel economy
- 5Check Engine Light is on or flashing
Common Causes of P0303
Parts most likely causing this code, ranked by probability
A failing ignition coil for cylinder #3 cannot provide enough spark to ignite the fuel-air mixture.
40% of P0303 cases are fixed by replacing the ignition coil
A worn, fouled, or damaged spark plug in cylinder #3 prevents proper ignition of the fuel.
35% of P0303 cases are fixed by replacing the spark plug
A clogged or faulty fuel injector for cylinder #3 fails to deliver the correct amount of fuel, leading to a misfire.
15% of P0303 cases are fixed by replacing the fuel injector
Low compression in cylinder #3, caused by issues like a bad valve, head gasket, or piston rings, prevents proper combustion.
8% of P0303 cases are fixed by addressing engine compression
Damaged wiring to the ignition coil or fuel injector, or a rare fault in the Powertrain Control Module (PCM), can cause a misfire.
2% of P0303 cases are fixed by repairing wiring or PCM
Check These First (Before Buying Parts)
- Visually inspect the ignition coil and spark plug for cylinder #3 for any obvious damage, cracks, or oil fouling.
- Listen for any unusual engine noises, especially ticking or knocking, which could indicate a deeper issue.
How to Diagnose P0303
- 1Check for a flashing Check Engine Light (CEL) – this indicates an active, damaging misfire.
- 2Inspect the spark plug and ignition coil for cylinder #3 for visible damage or fouling.
- 3Swap the ignition coil from cylinder #3 to another cylinder (e.g., #1) and see if the misfire code moves to the new cylinder (e.g., P0301).
- 4Swap the spark plug from cylinder #3 to another cylinder and see if the misfire code moves.
- 5Perform a fuel injector balance test or swap the fuel injector from cylinder #3 to another cylinder to check if the misfire follows.
- 6Conduct a compression test on cylinder #3 to check for internal engine issues.
P0303 on Popular Vehicles
Toyota Camry
2007-2024P0303 on a Toyota Camry often points to a failing ignition coil or a worn spark plug. These are straightforward to diagnose and replace. Less commonly, a clogged fuel injector can be the culprit.
75% fixed by replacing ignition coil or spark plug
Honda Accord
2003-2024Honda Accords with P0303 frequently experience issues with ignition coils or spark plugs. It's a common maintenance item. Check for oil in the spark plug tubes, which can foul plugs and coils.
70% fixed by replacing ignition coil or spark plug
Ford F-150
2004-2024Ford F-150s, especially those with Triton engines, are known for ignition coil failures causing P0303. Spark plugs can also be an issue, sometimes seizing in the cylinder head on older models.
78% fixed by replacing ignition coil or spark plug
Frequently Asked Questions
What does P0303 mean?
P0303 indicates that your vehicle's engine computer has detected a misfire specifically in cylinder #3. This means cylinder #3 is not firing correctly or contributing its share of power.
Can I drive with P0303?
Limit driving, fix within a few days. If the Check Engine Light is flashing, stop driving immediately. A flashing light means severe misfires are occurring, which can rapidly damage your catalytic converter. If the light is solid, you can drive for essential short trips, but prolonged driving will cause further damage and reduce fuel economy.
Will P0303 clear itself?
No, P0303 will not clear itself. The underlying issue causing the misfire must be diagnosed and repaired. Once the repair is complete, you can clear the code with an OBD-II scanner, or it will clear after several drive cycles if the problem is resolved.
How do I fix P0303 myself?
Start by inspecting the spark plug and ignition coil for cylinder #3. You can swap the ignition coil with another cylinder to see if the misfire moves. If not, try swapping the spark plug. If the misfire persists, check the fuel injector for cylinder #3. A compression test is the next step if ignition and fuel components are good.
How much does it cost to fix P0303?
DIY repair costs for P0303 typically range from $50 to $200, primarily for a new spark plug or ignition coil. Professional shop repairs can cost $150 to $500, depending on the part needing replacement and labor rates. More complex issues like a fuel injector or compression problem will increase costs.
P0303 keeps coming back - why?
P0303 keeps coming back because the root cause was not fully addressed. This often happens when only one component (like a spark plug) is replaced, but the actual problem is a failing ignition coil, a clogged fuel injector, or a deeper engine issue like low compression. A thorough diagnostic process is essential to pinpoint the exact cause.
Will P0303 fail emissions/smog test?
Yes, P0303 will cause your vehicle to fail an emissions or smog test. A misfire means unburned fuel is entering the exhaust, increasing harmful emissions. The Check Engine Light being on, even if not flashing, is an automatic failure in most emissions tests.
What's the difference between P0303 and P0300?
P0303 specifically indicates a misfire in cylinder #3. P0300, on the other hand, means a 'Random/Multiple Cylinder Misfire Detected,' indicating misfires are occurring in multiple cylinders or are moving between cylinders, making it harder to pinpoint a single faulty component.
P0303 on Honda Civic?
P0303 on a Honda Civic is commonly caused by a failing ignition coil or a worn spark plug for cylinder #3. These engines are generally reliable, but ignition components do wear out. Start by checking and swapping the ignition coil and spark plug for cylinder #3.
Questions to Ask Your Mechanic
Did you perform a compression test on cylinder #3?
Good answer: Yes, compression is X PSI, which is within specification. This rules out internal engine damage.
Did you swap the ignition coil and spark plug to confirm the misfire stays with cylinder #3?
Good answer: Yes, we swapped the coil and plug to different cylinders, and the misfire code remained on cylinder #3, confirming the issue is specific to that cylinder's fuel or compression.
What are the fuel trim readings for cylinder #3?
Good answer: Short-term and long-term fuel trims are within normal range, indicating the engine isn't over- or under-fueling globally, but we're checking the individual injector pulse width for cylinder #3.
Repair Cost Estimate
DIY Repair
Parts only
$50-$200
Shop Repair
Parts + labor
$150-$500
Save $100-$300 by doing it yourself
Difficulty
intermediate
Time
0.5-2 hours
Intermediate - requires basic mechanical skills, an OBD-II scanner, and careful diagnostic steps to avoid replacing the wrong part.
Cost of Waiting
Continued misfires send unburned fuel into your exhaust system, rapidly overheating and destroying your catalytic converter. A $50-$200 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 labor.
These rubber boots protect the spark plug from moisture and ensure a good connection. They can degrade over time, causing misfires. Replacing them with the coil or plug is a smart preventative measure.
Applying dielectric grease to the spark plug boot connections helps prevent corrosion, ensures a good electrical connection, and makes future removal easier.
Tools You'll Need
- OBD-II Scan Tool
- Spark Plug Socket Set
- Ratchet and Extensions
- Torque Wrench
- Spark Plug Gap Tool
- Multimeter (for testing coils/injectors)
- Compression Tester (if needed)
P0303 is a common and usually straightforward misfire code. Most repairs involve replacing an ignition coil or spark plug, getting your engine running smoothly again without breaking the bank.
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Your Next Steps
Step 1: Use an OBD-II scanner to confirm P0303 is the only code. Clear the code and see if it returns immediately.
Step 2: Perform a 'swap test' with the ignition coil and spark plug for cylinder #3. Move the coil to cylinder #1 and the plug to cylinder #2. If the code changes to P0301 (coil) or P0302 (plug), you've found your culprit.
Step 3: If the misfire remains on cylinder #3 after swapping ignition components, test the fuel injector for cylinder #3. You can swap it with another cylinder's injector to see if the misfire moves. If not, perform a compression test on cylinder #3.