OBD-II trouble code
P0301: Cylinder 1 Misfire Detected
The engine computer detected a misfire specifically in cylinder 1. Diagnosis is more targeted than P0300 — the bad part is on or feeding cylinder 1. The check engine light may be flashing; pull over if it is.
Quick facts
- System
- Powertrain
- Category
- Ignition and Misfire
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $50 – $1,500
- DIY difficulty
- Intermediate DIY
What does P0301 mean?
A misfire is a cylinder that fails to combust properly. The engine control module (ECM) detects misfires by monitoring crankshaft speed — a healthy combustion event accelerates the crankshaft slightly, and the ECM watches for the missing acceleration that signals a failed combustion event. When the ECM can isolate the misfire to a single cylinder, it sets a cylinder-specific code instead of P0300.
P0301 means the misfire is in cylinder 1. On an inline engine, cylinder 1 is typically at the front of the engine, closest to the timing components. On a V-configuration engine, cylinder 1 is on Bank 1 by definition, but its physical position varies by manufacturer — check the engine service information for the exact layout. Either way, the fault is in or affecting one specific cylinder.
A flashing check engine light during P0301 indicates the misfire is active. Unburned fuel reaches the catalytic converter and can damage it quickly. Pull over safely if the light is flashing. If the light is steady, you can usually drive directly to a shop — but skip hard acceleration and don't let the misfire continue for days.
Common causes
- Worn or fouled spark plug in cylinder 1
- Failing ignition coil for cylinder 1 (the most common cause on coil-on-plug engines)
- Faulty fuel injector for cylinder 1 (stuck, clogged, or leaking)
- Low compression in cylinder 1 from a burned valve, worn rings, or head gasket leak
- Cracked or damaged spark plug wire feeding cylinder 1 (on older engines with separate wires)
- Carbon buildup on the intake valve for cylinder 1
- Vacuum leak isolated to the cylinder 1 intake runner
- Bad spark plug gap from improper installation
Symptoms
- Check engine light on or flashing
- Rough idle and engine shaking
- Loss of power on acceleration
- Hesitation or stumble
- Poor fuel economy
- Smell of unburned fuel from the exhaust
- Engine running on three out of four cylinders (or five out of six, etc.)
Diagnostic steps
- 1.Confirm the code is P0301 and not P0300 — single-cylinder codes are diagnosed differently than random misfire codes.
- 2.Inspect the spark plug in cylinder 1. Compare its condition to the plugs in the other cylinders.
- 3.Swap the ignition coil from cylinder 1 with the coil from a known-good cylinder, clear the code, and drive. If the misfire moves to the new cylinder, the coil is bad. If P0301 returns, the coil is fine.
- 4.Do the same swap test with the spark plug.
- 5.Test the cylinder 1 fuel injector resistance, and use a noid light or scan tool to confirm it's pulsing.
- 6.If ignition and fuel test fine, perform a compression test on cylinder 1. Significantly lower compression points to a mechanical problem in the cylinder.
Repair cost
$50 – $1,500
A spark plug is $10 to $30 plus 15 to 30 minutes of labor for one cylinder. An ignition coil is $40 to $200 plus 15 minutes of labor. A fuel injector is $100 to $400 plus 1 to 3 hours of labor. Low compression repairs (valve job, head gasket) start at $1,000 and climb quickly.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with spark plug replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.