The Quick Answer above is the generic definition. What follows is what is documented for the Honda models that log P0300, checked against manufacturer data and owner reports.
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€60 - €700
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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 documented Honda-specific patterns:
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 2.8-4.1 bar (40-60 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 for P0300 in EUR, compiled across makes. Honda parts and labour usually land towards the lower end of each range.
Prices estimated as of March 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:
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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