OBD-II Code · Powertrain
P0301
Cylinder 1 Misfire Detected
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Depends on the light
Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise.
Indicative cost (USD)
$30–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Depending on part. Move the coil to a quiet cylinder first — that identifies the fault before you buy anything.
Cylinder 1 specifically is misfiring. The ECU detected that this cylinder isn't firing correctly — either no spark, no fuel, or compression issues.
How a shop works this
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing.
Photograph the coils before you touch anything, and note which is which.
Cylinder numbering is not the same across manufacturers, and V6 and V8 bank layouts differ by maker — look up the firing order and bank layout for your engine before you move parts, or you can spend an hour swapping coils on the wrong bank.
Move the cylinder 1 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 1, clear the code, and run it until the misfire returns.
On a modern coil-on-plug engine the coil is the most common single answer to a cylinder-specific misfire, which is why it is the first thing to move — not because it is the cheapest part. A misfire that is there even at idle is the classic dead-coil pattern.
- The misfire follows the coil to its new cylinderThe coil is the fault. Replace it. If the engine has real mileage on it, the other coils are on the same clock.
- The misfire stays on cylinder 1The coil is fine. Look at the coil connector and the harness around it next — chafed and rodent-damaged connections at that plug are a common second answer — then pull the plug.
Read the plug you pulled, and check the boot for carbon tracking.
Black and sooty means it has been running rich. White or blistered means lean or too hot. Oil-wet points at valve seals or rings. Fuel-wet points at an injector holding open. A carbon-tracked boot arcs to the head and imitates a dead coil for the price of a new boot. On an older engine with a distributor, the cap, rotor and plug wires belong in this step too.
If spark is accounted for, go to fuelling, then to compression.
An injector balance or flow test comes first because it is quicker. Compression test second: a cylinder more than about 15% below its neighbours is mechanical, and no ignition part will fix it. A vacuum leak on this one runner sits alongside these — a leak big enough to affect every cylinder would be setting P0300 instead.
A flashing check-engine light means the misfire is putting raw fuel into the catalytic converter, which can destroy it quickly. Stop driving as soon as it is safe to. A steady light with a mild misfire is less urgent, but stop anyway if it shakes hard, loses power, overheats, or makes a noise it was not making before.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Rough idle
- Engine stumble on acceleration
- Check engine light
- Smell of unburnt fuel
Likely causes
- Failed ignition coil (cylinder 1)Most common
- Damaged coil connector or harness at cylinder 1
- Worn spark plug or carbon-tracked boot (cylinder 1)
- Clogged or leaking fuel injector (cylinder 1)
- Low compression on cylinder 1
- Vacuum leak at the cylinder 1 intake runner
Read the full diagnostic procedureP0301 means the ECM detected a misfire on cylinder 1 specifically — it counts crankshaft deceleration events per cylinder firing event and flags any…
P0301 means the ECM detected a misfire on cylinder 1 specifically — it counts crankshaft deceleration events per cylinder firing event and flags any cylinder whose deceleration deviates from the expected pattern by more than the manufacturer's threshold (usually 2-4% of total firing events within a 1,000-rev window).
The diagnostic order on a shop floor
- pull the coil and plug from cylinder 1, inspect the plug for fouling (black/sooty = rich, white/blistered = lean, oil-wet = ring or valve seal failure, fuel-wet = injector stuck open), then swap that coil with cylinder 2's coil and clear the code.
- If the misfire moves to cylinder 2 on the next drive cycle, the coil is bad — $40-180 part.
- If the misfire stays on cylinder 1, swap the plug next; if it still stays, you're into compression test territory (looking for <15% variance between cylinders) and then injector flow/balance testing.
- Don't skip the visual on the coil boot — carbon-tracked boots arc to the head and mimic a dead coil for $15 worth of dielectric grease.
Vehicle-specific patterns2002-2008 Mini Cooper (R50/R53/R56) throws P0301 constantly because cylinder 1 sits closest to the firewall heat soak and cooks the coil first — the…
- 2002-2008Mini Cooper (R50/R53/R56) throws P0301 constantly because cylinder 1 sits closest to the firewall heat soak and cooks the coil first — the fix is almost always a single coil, but the smart play is replacing all four since the others are 80% of the way to failure.
- 2007-2014Ford Edge/Lincoln MKX with the 3.5L Duratec frequently throws P0301 from a cracked plastic intake manifold runner specifically over cylinder 1, causing a localized vacuum leak — smoke-test the intake before condemning the coil.
- 2003-2009Toyota 4Runner/Tacoma with the 1GR-FE 4.0L V6 commonly throws P0301 from carbon buildup on the intake valve of cylinder 1 (it's the longest runner from the throttle body, so it sees the leanest charge); a walnut-blast service clears it.
Estimated repair$40 (single coil DIY) to $1,800+ (head work for a burned valve).
Look up another code
P0301 — frequently asked
What does a P0301 code mean?
Cylinder 1 specifically is misfiring. The ECU detected that this cylinder isn't firing correctly — either no spark, no fuel, or compression issues.
What causes a P0301 code?
Common causes: Failed ignition coil (cylinder 1); Damaged coil connector or harness at cylinder 1; Worn spark plug or carbon-tracked boot (cylinder 1); Clogged or leaking fuel injector (cylinder 1); Low compression on cylinder 1; Vacuum leak at the cylinder 1 intake runner.
What are the symptoms of a P0301 code?
Typical symptoms: Rough idle; Engine stumble on acceleration; Check engine light; Smell of unburnt fuel.
Is it safe to drive with a P0301 code?
Depends on the light. Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise. Estimated repair: $30-$400 depending on part. Move the coil to a quiet cylinder first — that identifies the fault before you buy anything..
How do I diagnose a P0301 code?
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing. 1. Photograph the coils before you touch anything, and note which is which. 2. Move the cylinder 1 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 1, clear the code, and run it until the misfire returns. 3. Read the plug you pulled, and check the boot for carbon tracking. 4. If spark is accounted for, go to fuelling, then to compression.
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