Ford F-150 · Diagnostic Trouble Code
P0301 — Cylinder 1 Misfire Detected
What it means, how urgent it is, the most likely causes, and the exact order to diagnose it — with the repair guides that fix it.
What P0301 means
The PCM watches the crankshaft's rotation speed in tiny slices. Every cylinder's combustion pulse should push the crankshaft along evenly; when cylinder 1 fails to contribute its share, the crankshaft hesitates each time that cylinder comes up in the firing order. Once the pattern is consistent enough, the computer stores P0301 and turns on the check engine light.
A cylinder-specific code is actually good news diagnostically: it tells you exactly where to look, unlike P0300 (random misfire), which could be anything affecting the whole engine.
⚠️ How urgent is it?
A flashing check engine light with P0301: the misfire is severe right now. Raw fuel is reaching the exhaust and can melt the converter's internals in a single drive. Ease off, avoid hard acceleration, and get it checked immediately. If the engine shakes violently, stalls, or you smell strong fuel or rotten-egg odor, pull over and tow it.
Most likely causes
- Worn, fouled, or incorrectly gapped spark plug in cylinder 1 — the single most common cause.
- A failing ignition coil on cylinder 1.
- A clogged or failing fuel injector on cylinder 1.
- Low compression in cylinder 1 from a leaking valve, worn rings, or head gasket issue (less common, more serious).
- A vacuum leak near cylinder 1’s intake runner.
- Wiring or connector problems at the coil or injector for cylinder 1.
How to diagnose it — in order
-
1
Read freeze-frame data and check for companion codes. P0300 alongside it suggests a broader issue; P0171 points to a lean condition affecting that cylinder.
-
2
Inspect cylinder 1's spark plug. Pull it and check for worn electrodes, oil or carbon fouling, and cracks in the ceramic. Replace the full set if worn — plugs are cheap, labor is not.
-
3
Swap-test the ignition coil. Move cylinder 1's coil to another cylinder, clear the codes, and drive. If the misfire code follows the coil to the new cylinder, the coil is bad.
-
4
Test the fuel injector. If ignition checks out, listen to the injector with a stethoscope for a crisp click, or swap it like the coil to see if the misfire moves.
-
5
Check compression on cylinder 1. If ignition and fuel test good, a compression test reveals mechanical problems like leaking valves or worn rings.
-
6
Inspect the wiring. Look for chafed, melted, or oil-soaked wiring and loose connectors at cylinder 1's coil and injector.
Reading the code is step zero
A basic OBD2 scanner plugs into the port under your dash and tells you exactly which codes are stored — plus freeze-frame data showing what the engine was doing when the code set.
View OBD2 scanners on AmazonAs an Amazon Associate we earn from qualifying purchases.
Repair guides that fix P0301
General diagnostic information, not a factory service procedure. If you're unsure, have a qualified technician confirm the diagnosis before buying parts.