Where is cylinder 3 on my engine?

On most inline engines, cylinder 3 is the third position from the front. On V6 engines, cylinder 3 is often the last cylinder on Bank 1 in many configurations. On V8 engines, the position varies by manufacturer — Ford and GM number cylinders differently. Check the engine layout diagram in your service information.

Can I keep driving with P0303?

If the check engine light is flashing, stop driving when safe — the catalytic converter is at risk. With a steady light, drive directly to a shop and avoid hard acceleration. Don't let the misfire continue for more than a few days; even steady misfires accelerate catalyst wear.

Is P0303 worse on a V engine than an inline engine?

The code itself isn't worse, but on V engines the repair labor can be higher because accessing a rear cylinder may require removing the intake plenum or other components. Some V engines have hard-to-reach coils on the rear bank that take longer to swap or test.

How much does P0303 typically cost to fix?

Most cases land between $75 and $500 — a single plug, a coil, or an injector cleaning. V-engine cases that require removing the intake plenum can add a few hours of labor. Compression-related repairs start at $1,000.

OBD-II trouble code

P0303: Cylinder 3 Misfire Detected

The engine computer detected a misfire specifically in cylinder 3. Diagnosis is more targeted than P0300 — the bad part is on or feeding cylinder 3. The check engine light may be flashing; pull over if it is.

Quick facts

System: Powertrain
Category: Ignition and Misfire
Severity: High severity
Drivable: Usually safe to drive short-term
Repair cost range: $50 – $1,500
DIY difficulty: Intermediate DIY

What does P0303 mean?

A misfire is a cylinder that fails to combust properly. The engine control module (ECM) detects misfires by monitoring crankshaft speed — a healthy combustion event accelerates the crankshaft slightly, and the ECM watches for the missing acceleration that signals a failed combustion event. When the ECM isolates the misfire to a single cylinder, it sets a cylinder-specific code instead of the generic P0300.

P0303 means the misfire is in cylinder 3. On an inline engine, cylinder 3 is the third cylinder from the front. On a V6 in many configurations, cylinder 3 is the last cylinder on Bank 1. On a V8, cylinder 3 may be on Bank 1 or Bank 2 depending on the manufacturer — Ford and GM number their cylinders differently. Check your engine's service information for the specific layout.

A flashing check engine light during P0303 indicates the misfire is active. Unburned fuel reaches the catalytic converter and can damage it quickly. Pull over safely if the light is flashing. If the light is steady, you can drive directly to a shop, but avoid hard acceleration and address the code promptly.

Common causes

Worn or fouled spark plug in cylinder 3
Failing ignition coil for cylinder 3 (most common on coil-on-plug engines)
Faulty fuel injector for cylinder 3 (stuck, clogged, or leaking)
Low compression in cylinder 3 from a burned valve, worn rings, or head gasket leak
Cracked or damaged spark plug wire feeding cylinder 3 (older engines with separate wires)
Carbon buildup on the intake valve for cylinder 3
Vacuum leak isolated to the cylinder 3 intake runner
Wrong-gap or improperly seated spark plug

Symptoms

Check engine light on or flashing
Rough idle and engine shaking
Loss of power on acceleration
Hesitation or stumble
Poor fuel economy
Smell of unburned fuel from the exhaust
Audible miss at idle

Diagnostic steps

1.Confirm the code is P0303 alone — companion misfire codes (P0301, P0305) often point to a broader issue like a vacuum leak or low fuel pressure.
2.Inspect the spark plug in cylinder 3 and compare its condition to the other cylinders' plugs.
3.Swap the ignition coil from cylinder 3 with the coil from a known-good cylinder, clear the code, and drive. If the misfire follows the coil to its new location, the coil is bad.
4.Repeat the swap test with the spark plug.
5.Test the cylinder 3 fuel injector resistance and confirm pulse with a noid light or scan tool.
6.Perform a compression test on cylinder 3 if ignition and fuel components test fine.

Repair cost

$50 – $1,500

A single spark plug is $10 to $30 plus 15 to 30 minutes of labor. An ignition coil is $40 to $200 with brief labor. Fuel injector replacement is $100 to $400 plus 1 to 3 hours. On V engines, accessing a rear cylinder can require removing the intake plenum, which adds labor. Compression-related repairs run $1,000 and up.

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Open the Repair Cost Estimator with spark plug replacement preselected. Adjust labor rate and vehicle category to fit your situation.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.