Combustion qualitySafety screen firstReviewed September 6, 2026

P0301

301 code (P0301): Cylinder 1 misfire detected

A “301 code” usually means P0301: the engine computer detected a misfire in Cylinder 1. That tells you where to start testing, but it does not prove the spark plug, ignition coil, fuel injector, or engine itself is bad.

Also searched as: 301 code · Cylinder 1 misfire · P0301 engine code

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Evidence branches

Conditions that can produce P0301

These are diagnostic branches, not a ranked shopping list. Testing order depends on the exact vehicle and failure scene.

Spark plug, coil, boot, or ignition circuit
Injector, connector, or cylinder fuel delivery
Compression, leakage, valve, or valvetrain problem
Localized intake or coolant intrusion issue
Incorrect cylinder attribution or mechanical imbalance

Common symptoms

What drivers may notice

Symptoms can be absent, intermittent, or caused by another fault. Use them to preserve context—not to select a part.

Rough idle or shaking
Hesitation, weak acceleration, or reduced power
A flashing or steady check-engine light
Hard starting or stalling
Fuel odor or reduced fuel economy

Next checks

What to inspect next

Stop safely for a flashing lamp, severe vibration, overheating, or fuel odor
Compare Cylinder 1 counts with the other cylinders
Use controlled component substitution only when safe and documented
Confirm compression/leakage and injector control before replacing major parts

Cheapest-first path

Tests that separate the repair branches

Start with existing evidence and low-risk observations. A planning band describes diagnostic effort, not a guaranteed local price.

Preserve Cylinder 1 counts, freeze frame, and companion codes

Shows when the misfire occurs and whether it is isolated, load-related, temperature-related, or part of a larger pattern.

$0 with a capable scan

Inspect the plug, boot, coil connection, and accessible wiring

Finds basic installation, contamination, and connection evidence before substitution.

$0 visual check

Use a documented plug or coil swap when safe and appropriate

If the misfire follows the moved component, the test creates stronger evidence than replacing all ignition parts.

$0–$100 planning band

Verify injector command and cylinder compression or leakage

Separates fuel, electrical, valve, ring, head-gasket, and mechanical branches when ignition is not responsible.

$150–$400 diagnostic planning band

Evidence quality

What strengthens the answer

Cylinder counters under the failure conditionIgnition waveform or verified swap resultInjector command and balance resultCompression, leak-down, or in-cylinder evidence

Repair verification

Prove what changed

Preserve the pre-repair record, document exactly what changed, and repeat the relevant operating condition safely. Confirm that current or pending faults do not return, review permanent-code and readiness state where applicable, and state which tests or modules remained unavailable.

Cost planning

Possible P0301 repair ranges

These broad U.S. planning bands compare branches before tax; they are not quotes. Vehicle, access, parts, labor rate, region, related damage, and the confirmed test result control the real total.

Spark plug, boot, or single-coil branch

$75–$500

Exact plug access, coil design, and whether a full maintenance set is due affect the total.

Injector, connector, or localized intake branch

$250–$1,200

Require injector or leak evidence before authorizing the repair.

Compression, valve, head-gasket, or internal-engine branch

$1,000–$6,000+

Compression and leakage evidence must establish this branch; P0301 alone cannot.

Build a local cost worksheet

Direct answers

P0301 questions

What does P0301 mean?

The controller attributed a qualifying misfire pattern to Cylinder 1.

Does P0301 identify the broken part?

No. The cylinder number narrows the investigation but does not identify whether spark, fuel, compression, air distribution, wiring, or control is responsible. Confirm the exact vehicle definition and test the relevant branches before ordering a part.

Is it safe to drive with P0301?

Do not use the code alone to decide whether the vehicle is safe to drive. Stop and arrange qualified help for severe drivability, flashing warning lamps, smoke, fuel odor, overheating, braking or steering changes, electrical heat, or high-voltage damage.

How much does P0301 cost to repair?

The code alone cannot produce a defensible repair price. Cost depends on the confirmed cause, exact vehicle, parts choice, labor time, local labor rate, tax, supplies, and whether related damage is present.

What should I record before clearing P0301?

Record the reporting module, stored or pending status, freeze-frame data, readiness state, related codes, symptoms, battery voltage, and unavailable evidence. Clearing first can erase the most useful failure-scene context.

What does a 301 code mean?

People often say “301 code” when they mean P0301. It means the controller attributed a qualifying misfire pattern to Cylinder 1; it does not say whether the cause is spark, fuel, compression, wiring, air distribution, or control.

DEFINITION LIMIT

This page explains a commonly standardized code at a general level. Confirm the exact definition, module, status, test conditions, thresholds, wiring, and service process for the vehicle using current official information.

AUTHORSHIP · SOURCES · CORRECTIONS

See how this page earns trust.

These links are primary-source starting points for the page's scope. They do not replace the current manufacturer procedure, wiring, specification, or service information for a specific vehicle.

Publisher

ScanWrench Editorial is the working byline for this library. Joshua Black, founder and publisher, is responsible for publication decisions, disclosures, and corrections.

A reviewed date means an editorial scope and safety check. It is not an ASE credential, OEM authorization, or vehicle-specific repair approval.

Primary sources

SAE J2012 — Diagnostic Trouble Code DefinitionsSAE International · Standardized DTC structure, definitions, and manufacturer-controlled ranges.
SAE on-board diagnostics standards indexSAE International · Primary standards family for regulated OBD services, identifiers, and transport context.
OBD frequently asked questionsU.S. Environmental Protection Agency · Public explanation of regulated emissions diagnostics and the malfunction indicator light.

Revision history

September 6, 2026Reviewed edition: claim boundaries, safety language, internal links, and cited source scope checked.

No material correction is hidden. Material additions and corrections are dated above when they occur.

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