Can I drive with a P0303 cylinder 3 misfire?

With a solid check engine light and mild symptoms, you can drive carefully to the auto parts store for a free scan and to pick up spark plugs. A flashing check engine light means pull over immediately — severe misfires destroy catalytic converters.

I got both P0300 and P0303. Which do I fix first?

Start with cylinder 3 — P0303 identifies where the misfire is happening. Fix cylinder 3 (new plug, check the coil) and see if P0300 also clears. Often P0300 is set because the cylinder 3 misfire was frequent enough to look random to the ECM.

Where is cylinder 3 on my engine?

Cylinder numbering varies by engine layout. On most 4-cylinder front-wheel-drive cars (transverse mount), cylinders run 1–2–3–4 from the timing chain/belt end. On a V6, cylinder 3 may be on Bank 1 or 2 depending on the manufacturer. Search 'cylinder 3 location [your year make model]' or check the factory service manual.

How much does it cost to fix a P0303?

Spark plug only: $10 DIY, $80–$120 at a shop. Ignition coil: $35 DIY, $130–$200 at a shop. Injector: $50–$80 DIY (if accessible), $250–$400 at a shop. Compression issue: $1,500–$4,000 depending on root cause.

P0303moderate severityGenerally driveable

P0303 Code: Cylinder 3 Misfire Detected

What it means in plain English

P0303 is the same problem as P0301 — a cylinder misfiring — but cylinder 3 is the one that's stumbling. The engine isn't burning fuel cleanly in that cylinder, causing rough idle, loss of power, and sometimes a noticeable vibration. Because the ECM has pinpointed the exact cylinder, you know exactly where to start looking.

Most likely causes — ranked

#1 Worn or fouled spark plug in cylinder 3

most likely

Fix: Locate cylinder 3 on your specific engine (on most 4-cylinder transverse engines, counting from the timing chain/belt end: cyl 1–2–3–4; on inline engines from the front). Remove and inspect the plug. If it is oil-fouled, black, or the electrode is worn flat, replace the full set — plugs should always be replaced together.

DIY ~$10Shop ~$80

spark plugs repair guide

#2 Failed ignition coil for cylinder 3

likely

Fix: Swap the cylinder 3 coil with cylinder 1 or 4. Clear the code and run through a drive cycle. If the code changes to P0301 or P0304, the coil is confirmed bad — replace it. If P0303 stays, the coil is fine and the problem is the plug, injector, or mechanical.

DIY ~$35Shop ~$130

ignition coil repair guide

#3 Clogged or dead fuel injector on cylinder 3

possible

Fix: Add a bottle of high-quality fuel injector cleaner (Chevron Techron, BG44K) and drive a full tank. If the misfire clears, a dirty injector was the likely culprit. If it persists, the injector needs professional cleaning or replacement.

DIY ~$15Shop ~$300

fuel injector repair guide

#4 Low compression in cylinder 3 (worn piston rings or valve seat damage)

possible

Fix: A compression test on all four cylinders identifies a mechanically worn cylinder. Cylinder 3 reading more than 15–20 psi below others suggests internal wear. This is typically a shop repair; cost depends heavily on root cause (rings vs. valves vs. head gasket).

DIY ~$20Shop ~$2000

Get a FREE OBD2 scan first — no purchase required

AutoZone, O'Reilly Auto Parts, and Advance Auto Parts all scan your car's computer for free. Walk in, they plug in a scanner, you get a code in under 2 minutes. Then come back here and look up that code at eli5cars.com/obd2 for the plain-English explanation.

Pro tip: Take a photo of the code before they clear it.

P0303 Code: Cylinder 3 Misfire Detected

Most likely causes — ranked

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Frequently asked questions