EngineLightCodes
Powertrain code

P0303 Cylinder 3 Misfire Detected

Severity
Stop soon
Typical repair cost
$30–$880
Do it yourself
Possible, easy
Shop time
0.3–4 hours

Cylinder 3 is misfiring: its fuel isn't burning cleanly, so the engine runs rough and may lose some power. Most often the cylinder 3 ignition coil or spark plug is failing. On older engines with spark plug wires, a worn or loose plug wire is another common culprit.

How the engine computer detects it

The engine module detects misfire from crankshaft speed: a cylinder that does not fire gives no acceleration impulse. At a catalyst-damaging rate (CARB: at least 5 % per 200 revolutions) the warning light flashes; at an emissions-relevant rate (at least 1 % per 1,000 revolutions – GM about 2–5 %, Ford 0.9–1.5 %) it comes on after two trips. Ford and GM may shut off a misfiring cylinder's injector to protect the catalyst. P0303 means more than 90 % of the detected misfires fall on cylinder 3. Usual causes are the ignition coil or spark plug of that cylinder, its injector, or low compression; a quick test is to swap coil or plug with a neighbouring cylinder and see whether the misfire moves. Bulletins for four-cylinder engines name internal coil faults (Mazda) and plugs cracked during installation (FCA).

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light on, flashing at a catalyst-damaging rate
  • Rough idle, jerking, vibration
  • Loss of power, hesitation
  • Smell of unburnt fuel, higher consumption

Common causes

  1. Ignition coil of cylinder 3 faulty (coil, connector, ground) Most likely
  2. Spark plug of cylinder 3 worn, sooted, cracked or wrongly gapped Most likely
  3. Injector of cylinder 3 clogged or leaking, or its control Possible
  4. Low compression on cylinder 3 (valve, rings, head gasket) or local false air Less likely
  5. Water or oil in the plug well Less likely

How to diagnose P0303

  1. Find cylinder 3 using the numbering diagram for your engine. On a four-cylinder it's usually the second from the transmission end.
  2. If your engine has spark plug wires, check the cylinder 3 wire for cracks, burn marks or a loose fit, and swap it with a neighbor to see if the misfire moves.
  3. On coil-on-plug engines, swap the cylinder 3 coil with another cylinder's, clear the code and drive. Replace the coil if the misfire follows it.
  4. Pull the cylinder 3 spark plug and compare it with the others. One plug that looks very different from the rest points to a problem in that cylinder.
  5. If the ignition side is fine, have a shop test the cylinder 3 injector and run a compression or leak-down test.

Vehicles that report P0303 most

VehicleYearsReportsMedian miles
Ford Escape2006–20196692k
Ford Edge2016–20184162k
Chrysler Pacifica2017–202031—
Ford Fusion2013–201922103k
Honda CR-V2000–20222194k
Honda Accord2000–20241995k
Honda Odyssey2009–20191788k
Kia Soul2012–20221485k
Kia Sorento2014–20228—
Hyundai Tucson2017–20238—

Counts of owner complaints to the NHTSA that mention P0303 (395 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.

Reading the code

P
Powertrain
0
Generic (SAE) code
3
Ignition system or misfire
03
Specific fault

Questions drivers ask

Can I drive with code P0303?

A flashing check engine light means pull over and stop the engine as soon as it's safe. With a steady light, the car can usually make a short, gentle trip to a shop. Avoid hard acceleration, which makes a misfire worse.

Will my car pass an emissions inspection with P0303?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0303 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0303 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0303. They can point to a shared cause, so it's worth checking them together.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.