P0301: Cylinder 1 Misfire Detected
P0301 means the engine computer has detected a misfire in cylinder 1. The most common fix is replacing a worn spark plug, ignition coil, or a failed fuel injector, which usually costs about $150 to $450 at an independent shop, depending on the cause.
- Severity
- High
- Can I drive?
- Drive with caution
- DIY?
- Possible with some experience
- Repair cost range
- $150 – $2,500
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What does P0301 mean?
Cylinder 1 is not burning the air-fuel mixture the way it should on every engine cycle. When that happens, the engine shakes, loses power, and can send unburned fuel into the exhaust. The computer watches crankshaft speed and firing patterns, and it sets P0301 when it sees repeated misfires on cylinder 1. This code can be caused by ignition, fuel, air, or mechanical problems in that one cylinder.
Common symptoms
- Check engine light on or flashing
- Rough idle
- Engine shaking
- Hesitation when accelerating
- Loss of power
- Bad gas mileage
Causes, fixes and costs
P0301: Cylinder 1 Misfire Detected
General guide for most cars. Your car may differ.
A misfire can damage the catalytic converter if you keep driving, especially if the check engine light is flashing. Stop driving if the engine is shaking badly, power drops suddenly, or the light starts flashing.
Most likely causes
- 1
Worn spark plugHigh
A rough idle, hesitation, and a history of overdue tune-up service point to a worn or fouled spark plug in cylinder 1.
Quick check: Inspect the cylinder 1 spark plug for heavy wear, carbon fouling, oil, or a cracked insulator.
- 2
Failed ignition coilHigh
A misfire that gets worse under load, or one that moves when the coil is swapped to another cylinder, often points to a weak coil.
Quick check: Swap the cylinder 1 coil with another cylinder and see whether the misfire code follows the coil.
- 3
Bad fuel injectorMedium
A single-cylinder misfire with fuel smell, lean running, or a plug that looks dry and clean can point to an injector that is not delivering fuel.
Quick check: Listen for injector clicking and test injector resistance or pulse with proper diagnostic tools.
- 4
Low compression or valve problemMedium
If new plugs and coils do not help, and the engine misfires all the time at idle and under load, an internal engine problem may be the cause.
Quick check: Run a compression test or leak-down test on cylinder 1.
Can you fix it yourself?
Possible with some experience
Difficulty: Moderate. Basic tune-up parts and a scan tool can help you check the spark plug and coil, but fuel and compression testing usually need more experience. Ask the mechanic to diagnose cylinder 1 specifically, not just clear the code.
Show the stepsHide the steps
- Verify the code and note any other codes present
- Inspect and, if needed, replace the cylinder 1 spark plug
- Swap the cylinder 1 ignition coil with another cylinder and recheck the code
- Check the spark plug for oil, fuel, or coolant contamination
- Inspect the coil connector and wiring
- If ignition parts do not fix it, test the injector and compression
- Repair the underlying cause before clearing the code
Estimated repair cost
$150 – $350
Spark plug replacement for cylinder 1 or full tune-up: parts and labor; full set costs more than one plug
- Ignition coil replacement$180 – $450
- Fuel injector replacement$250 – $600
- Compression or valve repair$500 – $2,500
Prices vary by engine design, parts quality, and local labor rates.
Frequently asked questions
Can I drive with P0301?
You may be able to drive short distances if the engine runs mostly normally, but a misfire can damage the catalytic converter. If the check engine light is flashing or the engine is running very rough, stop driving.
Will P0301 clear itself?
It may turn off if the misfire stops for several drive cycles, but the cause is still there if the part is failing intermittently. If it comes back, the problem needs to be diagnosed.
What is the most common fix for P0301?
The most common fix is a spark plug or ignition coil problem on cylinder 1. On some engines, the fuel injector or a compression issue is the real cause.
Can a bad gas cap cause P0301?
No, a gas cap issue does not cause a cylinder 1 misfire code. P0301 points to a problem with how cylinder 1 is burning fuel.
Will P0301 fail emissions testing?
Yes, it often will if the check engine light is on or the engine is misfiring during inspection. Even if it passes a basic scan, a misfire should be fixed before the catalytic converter is damaged.
Related codes
Related problems
This guide covers most cars and is general advice, not an inspection. Prices are typical US independent-shop ranges and vary by region, car and shop. If your brakes, steering or a warning light feel unsafe, stop driving and contact a mechanic.