Motor Vehicle Expert
OBD fault code guide

P0301 Code Meaning UK

P0301 means cylinder 1 misfire detected. In simple terms, the engine computer has noticed that cylinder 1 is not firing properly. Common causes include a worn spark plug, faulty ignition coil, injector fault, wiring issue, air leak, low compression or a fuel delivery problem.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 Cylinder 1 misfire advice
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✓ Cylinder 1 misfire explained ✓ UK repair cost guide ✓ MOT-aware advice ✓ Mechanic-style checks
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Quick answer

What does P0301 mean?

P0301 means the ECU has detected a misfire on cylinder 1. A misfire happens when the air-fuel mixture in that cylinder does not burn properly, burns weakly or fails to ignite at the right time. The engine may shake, idle roughly, lose power, use more fuel or flash the engine management light.

Do not assume P0301 automatically means the spark plug is faulty. In real diagnostics, cylinder-specific misfires can be caused by ignition, fuel, air, compression, wiring or ECU-related faults. The best approach is to confirm whether the fault follows a swapped coil or plug, then check injector operation, wiring, fuel trims and compression if needed.

Most common cause

Ignition faults such as a worn spark plug or weak ignition coil are common, especially if the car shakes under load.

Most serious risk

A strong misfire can send unburnt fuel into the exhaust and damage the catalytic converter.

Best first check

Read all codes, check freeze-frame data and inspect cylinder 1 plug, coil, wiring and injector before replacing parts.

Symptoms

Common symptoms of a P0301 cylinder 1 misfire

The symptoms depend on how severe the misfire is and whether it happens at idle, under load, when cold or during acceleration.

Engine shaking or vibration

The engine may feel uneven, lumpy or shaky because one cylinder is not contributing properly.

Rough idle

The car may idle unevenly at traffic lights or feel like it is about to stall.

Flashing engine light

A flashing engine management light usually means an active misfire and should be treated as urgent.

Loss of power

The car may feel weak, hesitate or struggle when accelerating because cylinder 1 is not firing correctly.

Fuel smell or poor economy

Unburnt fuel from a misfire can increase fuel use and may create a fuel smell from the exhaust.

Hard starting or cutting out

A severe cylinder 1 misfire can make the engine difficult to start or cause stalling.

Likely causes

What causes P0301?

✅ Worn or fouled spark plug on cylinder 1.

✅ Faulty ignition coil or coil pack output.

✅ Injector fault, blocked injector or poor injector wiring.

✅ Vacuum leak or intake leak affecting cylinder 1.

✅ Low compression from valve, piston ring or head gasket issues.

✅ Fuel pressure or fuel quality problem.

✅ Wiring fault, connector corrosion or ECU driver issue.

Mechanic tip

Do not guess from the code alone

A P0301 code points to cylinder 1, but it does not prove which part has failed. A practical workshop check is to swap the cylinder 1 ignition coil with another cylinder and see if the misfire code moves. If the fault changes to P0302, P0303 or P0304, the coil is likely the issue. If the fault stays on cylinder 1, check the plug, injector, wiring, air leak and compression.

Read P0300 guide Misfire symptoms
Safe to drive?

Can you drive with a P0301 code?

It is not wise to keep driving with P0301 if the car is shaking, the engine light is flashing, power is reduced, the exhaust smells strongly of fuel or the engine feels like it may stall. A misfire can damage the catalytic converter and may leave you stranded.

⚠️ Stop driving soon if the engine light is flashing.

⚠️ Avoid motorway driving if the car is shaking or losing power.

⚠️ Do not ignore fuel smells, smoke or overheating.

✅ Short careful driving to a garage may be possible if the light is steady and the car runs normally.

Can you drive with engine light?
Catalyst risk

Why misfires can become expensive

When cylinder 1 misfires, unburnt fuel can enter the exhaust. The catalytic converter can overheat as it tries to burn that fuel inside the exhaust system. That is why a cheap ignition fault can become a much more expensive catalyst repair if ignored.

If P0301 appears with P0420, diagnose the misfire first before condemning the catalytic converter. Misfires can trigger catalyst efficiency faults.

P0420 catalyst guide
UK repair costs

Typical UK repair costs for P0301

Costs vary by vehicle, engine layout, labour time and whether the fault is ignition, fuel, wiring or mechanical.

Spark plug replacement

Typical range: £30–£120 depending on plug type and access.

Ignition coil replacement

Typical range: £80–£220 depending on vehicle and coil type.

Injector cleaning or test

Typical range: £80–£200 depending on testing and labour.

Fuel injector replacement

Typical range: £150–£450+ depending on engine and injector type.

Wiring or connector repair

Typical range: £60–£250 depending on fault tracing time.

Compression or engine repair

Typical range: £500+ if valve, piston, head gasket or internal engine work is needed.

Repair Costs Guide UK
Diagnosis flow

How to diagnose P0301 properly

1. Scan all modules

Record P0301 plus any related codes such as P0300, P0171, P0420 or oxygen sensor faults.

2. Check freeze-frame data

Look at RPM, load, coolant temperature and speed when the misfire happened.

3. Inspect cylinder 1 plug

Check for oil fouling, fuel wetness, worn electrodes, cracked ceramic or incorrect plug gap.

4. Swap coil or plug

Move the coil or plug to another cylinder and check whether the misfire follows.

5. Check injector and wiring

Listen for injector operation, check wiring and compare injector behaviour with other cylinders.

6. Test compression

If ignition and fuel checks pass, compression or leak-down testing may be needed.

MOT impact

Will P0301 fail an MOT?

The MOT test does not normally fail a car simply because a scan tool shows P0301, but the fault behind the code can cause a failure. If the misfire causes the engine management light to stay on, poor emissions, visible smoke, rough running or safety concerns, the vehicle may fail.

⚠️ High MOT risk: flashing engine light, rough running, high emissions or visible smoke.

⚠️ Medium risk: stored misfire with intermittent symptoms.

✅ Lower risk: repaired fault, no warning light and no running issue.

Engine light MOT guide Common MOT failures
Before buying a used car

P0301 on a car you want to buy

If a used car has P0301 stored, treat it as a negotiation or walk-away point until properly diagnosed. A seller may describe it as “just a spark plug”, but the same code can also point to injector, wiring or compression faults.

Before buying, check MOT history, service history, warning lights, test drive behaviour and whether the engine shakes at idle or under acceleration.

Used Car Buying Guides Inspection Checklist
Common mistakes

Mistakes to avoid with P0301

These are the mistakes that often turn a simple misfire into an expensive repair.

Replacing parts without testing

Do not fit plugs, coils and injectors blindly. Confirm what has actually failed.

Ignoring a flashing engine light

A flashing engine light usually means active misfire and possible catalytic converter damage.

Missing compression problems

If the fault stays on cylinder 1 after swapping ignition parts, compression testing may be needed.

Frequently asked questions

FAQs about P0301

Common questions about P0301 cylinder 1 misfire, safe driving, repair costs and MOT impact.

What does code P0301 mean?

P0301 means cylinder 1 misfire detected. The ECU has detected that cylinder 1 is not firing correctly compared with the other cylinders.

Is P0301 serious?

It can be serious. If the engine light is flashing or the car is shaking, stop driving and get it checked quickly to avoid catalyst damage.

Can a bad spark plug cause P0301?

Yes. A worn, fouled or damaged spark plug on cylinder 1 is a common cause, but it should be confirmed before parts are replaced.

Can an ignition coil cause P0301?

Yes. A weak or failing coil can cause cylinder 1 to misfire. Swapping the coil to another cylinder can help confirm the fault.

Can P0301 damage the catalytic converter?

Yes. An active misfire can send unburnt fuel into the exhaust, overheating and damaging the catalytic converter.

Should I clear the P0301 code?

Record the code and freeze-frame data first. Clearing it before diagnosis can remove useful information and make intermittent faults harder to trace.

About this guide

Written for practical UK fault finding

Motor Vehicle Expert explains diagnostic trouble codes in clear, mechanic-style language for UK drivers. This P0301 guide is designed to help you understand what cylinder 1 misfire detected means, what to check first and when the fault should be treated as urgent.

A fault code should always be used as a diagnostic starting point, not as a guaranteed parts list. Proper testing helps prevent unnecessary repairs.