P0303: Cylinder 3 Misfire Detected
Cylinder 3 is not burning its fuel properly.
Severity: 3 of 4
Park it if the light is flashing or the engine shakes badly. A misfire sends raw fuel into the exhaust and can destroy the catalytic converter. If the light is steady and the roughness is mild, drive gently and only as far as a shop or your driveway.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0303 means
The computer has counted repeated misfires in cylinder 3. It detects this by watching for a small dip in crankshaft speed each time cylinder 3 should fire.
Because the problem is isolated to one cylinder, the cause is usually a part that serves only that cylinder: its spark plug, ignition coil, or fuel injector. Less often it is a mechanical problem such as a leaking valve.
On inline engines, cylinder 3 is in the middle next to cylinder 2. Pooled oil in the plug tube is a common clue for a center cylinder misfire. On V engines, cylinder 3 location depends on the manufacturer's numbering. On some transverse V6 engines it is on the rear bank, which often requires removing the upper intake to reach the plug.
Which physical cylinder is number 3 depends on the engine. Your owner manual or a service manual shows the firing order layout. Do not guess on V engines, where numbering differs between manufacturers.
Common causes (cheapest likely first)
- Worn or fouled spark plug in cylinder 3. The cheapest likely fix. Check the gap and look for oil or carbon fouling.
- Failing ignition coil. The classic test is to swap the coil with a neighboring cylinder. If the misfire follows the coil to a new cylinder number, the coil is bad.
- Damaged plug wire or coil boot. Cracked boots let spark jump to the cylinder head instead of the plug.
- Clogged or leaking fuel injector. If the misfire stays with the cylinder after swapping coils and plugs, the injector is next.
- Low compression in that cylinder. A burnt valve, worn rings, or head gasket leak. A compression test confirms it.
Symptoms
- Flashing or steady check engine light
- Rough idle, often felt as a rhythmic shake
- Hesitation when accelerating
- Loss of power
- Fuel smell
DIY difficulty: Easy to moderate
Swapping a coil or plug is a good first DIY job when the cylinder is easy to reach. Rear cylinders on V engines can be hidden under the intake.
Tools: OBD-II scanner, Spark plug socket, Torque wrench, Dielectric grease, Compression tester for deeper checks
Cylinder 3 access and tips
- On inline engines, cylinder 3 is in the middle next to cylinder 2. Pooled oil in the plug tube is a common clue for a center cylinder misfire.
- On V engines, cylinder 3 location depends on the manufacturer's numbering. On some transverse V6 engines it is on the rear bank, which often requires removing the upper intake to reach the plug.
- If P0303 appears with P0302, inspect the center plug tubes for oil and replace the valve cover gasket and tube seals if needed.
- Mark the coil before swapping it to another cylinder so you can track which part moves where.
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Spark plug, one cylinder (most shops replace the set) | $8 to $30 | 0.2 to 1.5 h | $8 + 0.2 × $110 = $30 $30 + 1.5 × $190 = $315 |
| Ignition coil | $30 to $150 | 0.2 to 1.0 h | $30 + 0.2 × $110 = $52 $150 + 1.0 × $190 = $340 |
| Fuel injector | $50 to $250 | 1.0 to 3.0 h | $50 + 1.0 × $110 = $160 $250 + 3.0 × $190 = $820 |
Watch a repair video
Search YouTube for “P0303 fix” videos. Pick a recent video that matches your engine, and confirm the diagnosis before buying parts.
By make
This code works the same way on every make. See brand notes.
Repair manuals
Step-by-step service manuals with torque specs and wiring diagrams:
Haynes manuals Chilton manuals
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Related codes
Check for recalls
Before paying for a repair, enter your VIN in the NHTSA recall lookup. Emissions parts may also be covered by a federal emissions warranty; check your warranty booklet.
FAQ
How do I fix a P0303 misfire?
Start with the spark plug and the coil swap test. If the misfire moves with the coil, replace the coil. If it stays, try the plug, then test the injector and compression.
Can I keep driving with one misfiring cylinder?
Not for long. Even a steady light misfire damages the catalytic converter over time and can wash oil off the cylinder wall.
Should I replace all coils if one fails?
Not necessarily. Replacing just the failed coil is fine. Some owners replace all of them on high mileage engines to avoid repeat visits.
Where is cylinder 3 on my engine?
It depends on the engine. On inline engines numbering usually starts at the timing end. V engines vary by manufacturer. Check your service manual or the diagram on the intake cover.