Worn or fouled spark plug on cylinder 4, especially on Honda engines with high mileage or extended service intervals; Failed ignition coil or coil-on-plug boot for cylinder 4, a common failure on Honda four-cylinder engines; A clogged or failing fuel injector on cylinder 4 causing a lean or uneven fuel delivery; Low compression on cylinder 4 from worn piston rings, a burned valve, or a leaking head gasket; Vacuum leaks or intake manifold gasket leaks near cylinder 4 that lean out that specific runner; A faulty PCM or wiring issue in the cylinder 4 ignition coil circuit, though this is less common; Mechanical valvetrain problems such as a worn rocker arm or a sticking valve on cylinder 4

DTC codes / Honda codes / P1304

P1304 · HondaCylinder 4 Misfire

Q: What does code P1304 mean?

Cylinder 4 Misfire. P1304 on a Honda means the powertrain control module (PCM) has detected a misfire specifically on cylinder 4, usually by monitoring crankshaft speed fluctuations that occur when that cylinder fails to contribute power. The code is set when the misfire count exceeds a threshold that can damage the catalytic converter, and it often accompanies a flashing check engine light during the misfire event.

P1304 on a Honda means the powertrain control module (PCM) has detected a misfire specifically on cylinder 4, usually by monitoring crankshaft speed fluctuations that occur when that cylinder fails to contribute power. The code is set when the misfire count exceeds a threshold that can damage the catalytic converter, and it often accompanies a flashing check engine light during the misfire event.

SystemPowertrain

Code typeHonda specific

SeverityHigh

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

A steady or flashing check engine light, with flashing indicating a misfire severe enough to damage the catalytic converter
Noticeable engine shaking or vibration at idle that may smooth out at higher rpm
Rough running, hesitation, or a distinct loss of power under acceleration
A pungent rotten-egg smell from the exhaust if unburned fuel reaches the catalytic converter
Poor fuel economy and a richer-running engine as the PCM adds fuel to compensate
Often no symptoms besides the warning light when the misfire is intermittent or only occurs under specific load conditions

Common causes, most likely first

Worn or fouled spark plug on cylinder 4, especially on Honda engines with high mileage or extended service intervals
Failed ignition coil or coil-on-plug boot for cylinder 4, a common failure on Honda four-cylinder engines
A clogged or failing fuel injector on cylinder 4 causing a lean or uneven fuel delivery
Low compression on cylinder 4 from worn piston rings, a burned valve, or a leaking head gasket
Vacuum leaks or intake manifold gasket leaks near cylinder 4 that lean out that specific runner
A faulty PCM or wiring issue in the cylinder 4 ignition coil circuit, though this is less common
Mechanical valvetrain problems such as a worn rocker arm or a sticking valve on cylinder 4

How to diagnose and fix it

Scan all stored codes and freeze-frame data, then perform a cylinder balance test or misfire counter check to confirm cylinder 4 is the only affected cylinder
Inspect the spark plug on cylinder 4 for fouling, wear, or incorrect gap, and replace it if worn or damaged
Swap the ignition coil from cylinder 4 with a known-good coil from another cylinder and see if the misfire follows the coil
Check the fuel injector on cylinder 4 by listening for a consistent click or performing an injector balance test, and clean or replace it if necessary
Perform a compression test and a cylinder leak-down test on cylinder 4 to rule out mechanical faults such as bad rings or valves
Smoke-test the intake system to find vacuum leaks that could affect cylinder 4 specifically
Inspect the wiring harness and connector at the cylinder 4 ignition coil and injector for corrosion, chafing, or loose pins

Cylinder 4 misfire traps Honda owners fall into

A P1304 code on a Honda is often caused by a failing ignition coil that tests fine when cold but breaks down under load, so a simple resistance check may not reveal the fault.
Honda V6 engines with variable cylinder management (VCM) can set a cylinder 4 misfire when the VCM system disables cylinders, and the misfire may be a symptom of a faulty VCM solenoid rather than a bad plug or coil.
A dirty or failing mass airflow sensor (MAF) can cause a lean condition that affects cylinder 4 more than others, setting a misfire code without any ignition component being at fault.
A leaking intake manifold gasket on Honda engines often causes a misfire on a single cylinder, and the leak may only appear when the engine is cold or at idle.
Do not replace the catalytic converter based on a P1304 alone; the misfire must be repaired first, and the converter may recover once the misfire stops.

Can I keep driving with P1304?

If the check engine light is flashing, stop driving immediately and have the vehicle towed, because a flashing light means the misfire is severe enough to overheat and destroy the catalytic converter. If the light is steady, you can drive cautiously to a repair shop, but avoid hard acceleration and prolonged driving until the misfire is diagnosed.

Tools that help

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Guidance is general and written for Honda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.