P0300 means the engine computer has detected misfires across several cylinders without being able to pin them to one specific cylinder, so it flags the whole engine rather than a single cylinder. The most common trigger is worn or fouled spark plugs that no longer spark reliably, and a full set costs 40 to 150 EUR fitted. A steady light is a warning, but a flashing light means raw fuel is reaching the catalytic converter, so stop driving.
DTC/P0300·Honda
P0300 on Honda: Causes, Symptoms and Fix Cost
Quick Answer
High SeverityNot safe to driveHonda
P0300 on a Honda means the engine computer has detected misfires across several cylinders without being able to pin them to one specific cylinder, so it flags the whole engine rather than a single cylinder. The most common trigger is worn or fouled spark plugs that no longer spark reliably, and a full set costs 40 to 150 EUR fitted. A steady light is a warning, but a flashing light means raw fuel is reaching the catalytic converter, so stop driving.
Repair cost on Honda€54 - €630
What does P0300 mean on a Honda?
Honda Civic
2006-2024The 1.5L turbo (L15B7) in 2016 and newer Civics has a documented fuel-dilution issue where petrol thins the engine oil and causes misfires and P0300, especially on short cold trips, and Honda released a software update to reduce it, so check the oil level and smell it for fuel. Earlier R18A engines commonly need a valve-clearance adjustment around 100,000 km to stop tight valves causing misfires.
What causes P0300 on a Honda?
Beyond the generic causes listed on the main P0300 page, these are the Honda-specific patterns we see most often:
Honda CivicFuel dilution on the 1.5L turbo (2016+), check oil level and smell for petrol
Honda CivicValve clearance adjustment needed on R18A engines near 100,000 km
How to diagnose P0300 on a Honda with OBD2
Follow these steps to pinpoint the root cause of P0300:
- Scan for companion codes (P0301 to P0312). If a cylinder-specific code is also stored, start with that cylinder before treating P0300 as a whole-engine fault
- Inspect the spark plugs for wear, oil or carbon fouling, and a worn electrode gap. Replace the full set if they are over 50,000 km old or if several look fouled
- Test the ignition coils, swapping one coil to a different cylinder to see if the misfire follows it, or measuring resistance with a multimeter against spec
- Smoke-test the intake for vacuum leaks, or spray carb cleaner around the intake manifold gasket and hoses and listen for an idle change
- Check fuel pressure with a gauge. It should hold steady at the maker's spec, typically around 40 to 60 PSI on port-injection engines, and not drop under load
- Inspect the EGR valve for sticking and check intake valves for carbon on direct-injection engines, then run a compression or leak-down test if everything else checks out
How much does P0300 cost to fix on a Honda? (EUR)
Estimated repair costs on a Honda (Honda parts and labour typically run 10% below the average for this code).
Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0300 on Honda
These codes commonly cluster with P0300 on Honda vehicles:
FAQ: P0300 on Honda
What does the P0300 code mean?
P0300 stands for Random/Multiple Cylinder Misfire Detected. The engine computer monitors crankshaft speed and has seen misfires on two or more cylinders, but no single cylinder is failing badly enough to earn its own code. It points to a fault affecting the whole engine, such as ignition, fuel supply, or a vacuum leak, rather than one bad cylinder.
What are the symptoms of P0300?
The most common signs are a rough or shaking idle, hesitation when you accelerate, a loss of power under load, harder cold starts, and worse fuel economy. The check engine light may glow steadily or flash. A flashing light during the misfire is the serious case, it means raw fuel is reaching the catalytic converter.
What causes a P0300 code?
The usual culprits, in rough order, are worn spark plugs, failing ignition coils, a vacuum leak at the intake, weak fuel delivery from a tired pump or clogged injectors, carbon buildup or a stuck-open EGR valve, and, less often, low compression from a head gasket or worn rings. Because several cylinders are affected, look for one shared cause rather than four separate faults.
Is it safe to drive with a P0300 code?
It is not recommended. With a steady light you can usually drive a short distance to a garage gently, but with a flashing light you should stop as soon as it is safe. Active misfires push unburned fuel into the exhaust, which can overheat and ruin the catalytic converter within minutes, turning a plug job into a far larger repair.
How do you fix and clear a P0300 code?
Fix the underlying cause first, most often a fresh set of spark plugs and any failed ignition coil, then a vacuum leak or fuel issue if those are not it. Once the repair is done, the code can be cleared with a scan tool, or many cars clear it themselves after several drive cycles with no new misfires. Clearing the code without fixing the fault only makes it return.
How much does it cost to fix a P0300?
It depends entirely on the cause. A full set of spark plugs is around 40 to 150 EUR fitted, and a single ignition coil runs about 40 to 200 EUR. A vacuum leak is often cheap parts but labour-heavy, and a fuel injector or compression-related repair can run several hundred euros. Diagnosing it correctly first is what keeps the bill down.
Looking for the full P0300 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0300 guideSkanyx · Honda
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