What is the code P0304 on a 2012 Honda Pilot?

P0304 indicates a misfire in cylinder 4.

On a 2012 Honda Pilot, this means the engine control unit has detected that the fourth cylinder is not firing properly, which can be caused by ignition, fuel delivery, or mechanical issues. A misfire can reduce power, hurt fuel economy, cause rough running, and over time damage the catalytic converter if left unresolved.

What P0304 means on a 2012 Honda Pilot

P0304 is one of several cylinder-specific misfire codes in the OBD-II system. It signals that the engine management computer has detected a failure to ignite the air-fuel mixture in cylinder 4. The misfire may be intermittent or persistent and can occur under idle or load, sometimes accompanied by a rough idle or hesitation.

Common causes

Below are the typical culprits that can trigger a P0304 in the Honda Pilot’s 3.5-liter V6. Each item represents a different part of the ignition, fuel, or engine mechanics that could be at fault.

• Worn or fouled spark plug in cylinder 4


• Faulty ignition coil or coil-on-plug for cylinder 4


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• Low fuel pressure or fuel delivery problems affecting cylinder 4


• Vacuum leak or intake manifold gasket issue near cylinder 4


• Compression problems in cylinder 4 (valve seating, piston rings, or head gasket)


• Damaged wiring or connectors to the spark plug/coil or injector

Addressing these causes typically starts with a visual inspection and targeted replacements, followed by functional tests of fuel and ignition components. If the misfire persists after these steps, more advanced diagnostics may be required.

How technicians diagnose P0304 in a 2012 Honda Pilot

To isolate the source of the misfire, technicians follow a structured diagnostic process. The steps below outline a common approach used by shops and independent mechanics.

1. Confirm codes and review freeze frame data with an OBD-II scanner to verify P0304 and check for related codes (such as P0300).


2. Inspect the spark plug in cylinder 4 for wear, fouling, or improper gap; replace if necessary.


3. Perform a coil swap test by moving the ignition coil from cylinder 4 to another cylinder (and vice versa) to see if the misfire follows the coil.


4. Test the fuel injector on cylinder 4 for proper operation, including electrical resistance and spray pattern; listen for injector activity with a stethoscope or use a noid light to confirm signal.


5. Check for vacuum leaks around the intake manifold or around cylinder 4 that could cause lean misfire conditions; a smoke test can help identify leaks.


6. Measure fuel pressure to ensure the system is delivering the correct pressure to all cylinders, and perform a compression test on cylinder 4 to assess mechanical health.

After these steps, the technician will review all findings to determine whether the fix is a simple component replacement or if more extensive engine work is required. If the misfire is persistent, do not ignore it, as prolonged running with a misfiring cylinder can damage the catalytic converter and reduce engine performance.

What to do if you see P0304

If your 2012 Honda Pilot shows the check engine light with P0304, consider the following actions. If you are comfortable with basic maintenance, you can start by inspecting and replacing the spark plug in cylinder 4 and inspecting the related coil. If you notice persistent rough idle, hesitation, or reduced power, or if you hear irregular noises, stop driving the vehicle and seek a professional diagnosis promptly.

Special considerations for the 2012 Honda Pilot

The Pilot’s 3.5-liter V6 uses coil-on-plug ignition and individual fuel injectors for each cylinder. Misfires on one cylinder can be caused by a fault in any of these components or by a mechanical issue in that cylinder. Given the vehicle’s age, corrosion in connectors, buildup in injectors, and worn ignition components are common culprits. Addressing misfires early helps protect the catalytic converter and maintain safe, reliable operation.

Summary

P0304 is a cylinder 4 misfire code on a 2012 Honda Pilot. The issue may stem from ignition, fuel delivery, vacuum leaks, or mechanical problems in cylinder 4. A systematic diagnostic approach—checking spark, coil, injector, fuel pressure, and compression—helps identify the root cause. Prompt attention can prevent further damage and restore engine performance. If in doubt, consult a qualified technician for a precise diagnosis and safe repair.