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P0301 — Cylinder 1 Misfire

P0301 is set when the engine control module's misfire monitor detects that combustion is failing specifically in cylinder 1. The ECM identifies the affected cylinder by correlating crankshaft deceleration with camshaft position. The fact that only cylinder 1 is misfiring narrows the cause to parts that are specific to that cylinder — its plug, coil, injector, compression, or in some cases its harness wiring.

P0301 means cylinder 1 misfire. Stop driving and diagnose it before continuing — it can signal an unsafe condition. The most common cause is failed ignition coil on cylinder 1 (typically $80–$450). Causes and cost vary by make and model; confirm the root cause before replacing parts.

Severity: high powertrain Do not drive

Reviewed by MECH AI Editorial · Last verified

What does P0301 mean?

P0301 is set when the engine control module's misfire monitor detects that combustion is failing specifically in cylinder 1. The ECM identifies the affected cylinder by correlating crankshaft deceleration with camshaft position. The fact that only cylinder 1 is misfiring narrows the cause to parts that are specific to that cylinder — its plug, coil, injector, compression, or in some cases its harness wiring.

What are the symptoms of P0301?

What causes P0301?

Cause Likelihood Estimated repair (USD)
Failed ignition coil on cylinder 1 — On coil-on-plug engines this is the single most likely cause. Most common $80–$450
Worn, fouled, or wrong-gap spark plug in cylinder 1 Most common $15–$80
Clogged, leaking, or electrically failed injector on cylinder 1 Common $150–$800
Burnt exhaust valve or low compression on cylinder 1 Occasional $800–$3,500
Damaged or chafed wiring to the cylinder 1 coil or injector Occasional $80–$300
Cracked cylinder 1 intake runner or local vacuum leak Rare $100–$600

Repair costs are typical US ranges and vary by make, model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.

Is it safe to drive with P0301?

No. P0301 is a high-severity code — avoid driving until it is diagnosed and repaired, as it can indicate an unsafe condition or risk further damage.

How to diagnose P0301

  1. Confirm cylinder 1 location on this engine

    Cylinder 1 numbering differs by manufacturer. On most inline engines cylinder 1 is at the front. On most transverse V6s cylinder 1 is on the bank closer to the firewall. Consult the service manual before pulling parts.

    Tools: Vehicle-specific service information

  2. Swap the cylinder 1 ignition coil with a known-good cylinder

    Move the cylinder 1 coil to cylinder 2 (or any non-misfiring cylinder), and move that coil to cylinder 1. Clear codes and drive. If the misfire follows the coil to its new cylinder, replace the coil. If the misfire stays in cylinder 1, the coil is fine.

    Tools: Socket set

  3. Swap the cylinder 1 spark plug

    Use the same swap method with the spark plug. Inspect the removed plug first — a wet, fuel-soaked plug means no spark or no compression; a black sooty plug means a rich condition; a cracked ceramic means replace immediately.

    Tools: Spark plug socket, Extension and ratchet

  4. Test the cylinder 1 injector electrically and acoustically

    Listen to the injector with a stethoscope at idle — it should click rhythmically. A "noid light" or scan tool fuel-injector test confirms that the ECM is firing the injector. If it pulses but the cylinder still misfires, the injector may be clogged or leaking.

    Tools: Mechanic's stethoscope, Noid light kit or scan tool injector test

  5. Perform a wet/dry compression test on cylinder 1

    Measure compression on cylinder 1 cold and warm. If significantly lower than the other cylinders, add a teaspoon of oil through the plug hole and retest. Pressure that rises with oil points to worn rings; pressure that stays low points to valves or the head gasket.

    Tools: Compression tester, Engine oil

How do I fix P0301?

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P0301: frequently asked questions

What does diagnostic trouble code P0301 mean?

P0301 is set when the engine control module's misfire monitor detects that combustion is failing specifically in cylinder 1. The ECM identifies the affected cylinder by correlating crankshaft deceleration with camshaft position. The fact that only cylinder 1 is misfiring narrows the cause to parts that are specific to that cylinder — its plug, coil, injector, compression, or in some cases its harness wiring.

What are the symptoms of P0301?

Check Engine Light steady or flashing depending on misfire severity. Distinct rough idle that smooths out at higher RPM. Stumble or hesitation under acceleration. Reduced engine power. Smell of unburned fuel from the exhaust. Faint exhaust pop or backfire on overrun in severe cases

What causes P0301?

Failed ignition coil on cylinder 1 (most-common). Worn, fouled, or wrong-gap spark plug in cylinder 1 (most-common). Clogged, leaking, or electrically failed injector on cylinder 1 (common). Burnt exhaust valve or low compression on cylinder 1 (occasional). Damaged or chafed wiring to the cylinder 1 coil or injector (occasional). Cracked cylinder 1 intake runner or local vacuum leak (rare)

Is it safe to drive with P0301?

No. P0301 is a high-severity code — avoid driving until it is diagnosed and repaired, as it can indicate an unsafe condition or risk further damage.