P0301
Cylinder 1 Misfire Detected
Misfires concentrated on cylinder 1. A cylinder-specific code points away from shared causes (fuel pressure, MAF) toward components dedicated to that cylinder — coil, spark plug, injector, compression.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
What we see in the workshop
ON FORD ECOBOOST
A cylinder-specific misfire on an EcoBoost usually means a coil or plug, but on a hard-driven or tuned car we also check for carbon on that cylinder and compression before signing it off.
ON ALFA ROMEO
On the 1.4 MultiAir, a persistent single-cylinder misfire that survives new coils and plugs points toward the MultiAir brick.
Symptoms
- Check engine light on or flashing
- Rough idle and uneven running
- Power loss, hesitation under acceleration
- Increased fuel consumption
- Possible smell of unburned fuel from exhaust
Common causes
Ordered by how often each turns out to be the cause.
- Ignition coil for cylinder 1 failedCommon
- Spark plug for cylinder 1 worn or fouledCommon
- Cylinder 1 injector cloggedPossible
- Low compression on cylinder 1Less likely
Parts involved
- Ignition Coil
- Spark Plug
- Fuel Injector
P0301 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.