P0301 Cylinder 1 Misfire on Honda & Acura: Causes, Fixes & Cost
In short
P0301 on a Honda or Acura means cylinder 1 specifically is misfiring. Because it's pinned to one cylinder, the cause is almost always on that cylinder — a worn spark plug, a failing ignition coil, an oil-fouled plug from a leaking valve-cover/tube seal, or a clogged injector. On Honda engines, oil leaking down the spark-plug tubes is a classic culprit, and some 2016-2019 1.5T Civic/CR-V engines had injector-related service updates worth checking before you pay for parts.
Is it safe to drive with P0301-honda?
A steady light with a mild single-cylinder misfire is usually okay for a short, gentle drive to get it repaired. A FLASHING check engine light means raw fuel is reaching the catalytic converter and can destroy it — stop driving. Even a steady misfire shouldn't sit for weeks, since it overheats and damages the cat over time.
Symptoms
- Check engine light on, sometimes flashing under load
- Rough idle and a noticeable vibration
- Hesitation or stumble on acceleration
- Slight loss of power
- Reduced fuel economy
- Occasional smell of unburnt fuel
Common causes (most → least likely)
How to diagnose it (before buying parts)
- 1 Locate cylinder 1 for your specific Honda/Acura engine (it is not always nearest the front) using the firing-order diagram.
- 2 Pull the cylinder 1 coil and plug. Look for oil in the spark-plug well — if it's wet with oil, you have a leaking valve-cover gasket or tube seals fouling the plug, which must be fixed, not just the plug.
- 3 Swap the cylinder 1 ignition coil to an adjacent cylinder and clear the code. If the misfire follows the coil (becomes P0302, etc.), replace the coil; if it stays on cylinder 1, the coil is fine.
- 4 Inspect the plug for fouling, a wide gap, or cracked porcelain. Use OEM NGK/Denso plugs gapped to spec.
- 5 If ignition checks out, look at the injector (balance/buzz test). On 2016-2019 1.5T Civic/CR-V, check for any open injector or oil-dilution service update before buying parts.
- 6 If ignition and fuel are ruled out, do a compression and leak-down test on cylinder 1 for a mechanical fault.
Repair options & cost
By manufacturer
On higher-mileage Civic, Accord, CR-V and Odyssey, check the spark-plug well for oil first — a leaking valve-cover gasket or tube seals fouls the plug and causes a stubborn single-cylinder misfire. Use OEM NGK/Denso plugs gapped to spec; off-brand plugs are a common repeat-misfire cause.
Acura V6s (TL, MDX, RDX) follow the same pattern — coil or plug first, then check for oil in the wells. Replace coils with OEM parts and verify the plug gap.
These turbo engines had documented fuel-injector and oil-dilution service campaigns. Before paying for an injector, check whether your VIN qualifies for an extended warranty or a software/injector update at the dealer.
Frequently asked questions
Why does my Honda keep misfiring on cylinder 1 after a new plug?
A very common Honda cause is oil leaking into the spark-plug well from a worn valve-cover gasket or tube seals. The oil fouls the new plug and the misfire returns. Fix the leak and reseal the wells, not just the plug.
How do I confirm it's the coil and not the plug?
Swap cylinder 1's coil to a neighboring cylinder and clear the code. If the misfire moves with the coil, replace the coil. If it stays on cylinder 1, the coil is fine and you look at the plug, oil-fouling, injector, or compression.
My 2016-2019 1.5T Civic/CR-V has P0301 — is it the injector?
It can be. These engines had injector and oil-dilution service updates. Before buying an injector, check whether your vehicle qualifies for an extended warranty or dealer software/injector update — it may be covered.
Is P0301 expensive to fix on a Honda?
Usually not. The common fixes are a spark plug or one ignition coil — often under $100 in parts. Resealing oily spark-plug wells is a moderate job, and only a fuel-injector or mechanical cause pushes the cost higher.