P0300 on Genesis: How to Diagnose & Fix
Random/Multiple Cylinder Misfire Detected
3 Genesis models · 4 documented issues · $300-$1,500 repair
P0300 on Genesis by model: symptoms, diagnosis and fix
The 5.0L Tau V8 is gasoline-direct-injection only (no port injectors to wash the valves), so intake valves accumulate carbon deposits over time, which can cause rough idle, misfire and reduced performance at higher mileage. Some 2018+ owners also report elevated oil consumption (adding oil between changes), though rates are often within Genesis's acceptable spec.
Common Symptoms
- Rough idle
- Cold-start misfire/stumble
- Reduced power at higher mileage
- Needing to add oil between changes
- Check-engine light for misfire
How to Fix
Perform periodic walnut-blast (media) cleaning of the intake valves to remove carbon; use Top Tier 91-93 octane fuel and occasional higher-rpm driving to slow deposit formation, plus an intake-cleaning additive service. Monitor oil consumption with regular level checks between changes; document consumption for warranty if it exceeds spec.
Sources for this issue (1)
Some 3.3T owners report elevated engine-oil consumption — in one documented case roughly 2 quarts over a ~320-mile trip, accompanied by bluish exhaust smoke indicating oil burning. The consumed oil contributes to heavy intake-valve carbon (the 3.3T is direct-injected), sooty/wet spark plugs, and multi-cylinder misfire codes. Consumption is intermittent across the fleet (many cars use little to no oil), so owners should monitor levels between changes rather than assume the engine is unaffected.
Common Symptoms
- Oil level dropping noticeably between changes
- Bluish/grey exhaust smoke, especially on startup or under load
- Low-oil warning earlier than expected
- Fouled (sooty/wet) spark plugs and misfire codes
- Heavy intake-valve carbon found at service
How to Fix
Document consumption with a dealer oil-consumption test (measured top-offs over a set mileage) while the powertrain warranty is in force. Inspect the PCV system and turbo seals for oil ingestion, replace fouled spark plugs, and clean carboned intake valves (walnut blast) if buildup is found. Check the oil level frequently between changes and use the correct spec oil; severe consumption may require dealer powertrain repair under warranty.
Sources for this issue (1)
Like most gasoline direct-injection engines without supplemental port injection, the G70's 2.0T and 3.3T accumulate carbon on the backs of the intake valves over time because no fuel washes them. Owners report heavy valve coking by ~24,000 miles in some cases, especially when combined with oil consumption. The deposits disrupt airflow and seating, causing rough idle, hesitation, cold-start stumble, and cylinder misfire codes. Removing the intake to walnut-blast the valves is the definitive fix.
Common Symptoms
- Rough or uneven idle, especially cold
- Hesitation / stumble at low speed
- Cylinder misfire codes, sometimes a check engine light
- Reduced fuel economy and power
- Hard / rough cold start
How to Fix
Definitive repair is mechanical intake-valve cleaning (walnut-blasting / media blasting) after removing the intake manifold — typically due around 40,000-80,000 miles depending on driving and oil use. Address any contributing oil consumption (PCV/valve guides) at the same time. A quality top-tier fuel, regular oil changes, and an occasional Italian tune-up slow accumulation; catch-can installation reduces future buildup. Replace fouled spark plugs and clear misfire codes after cleaning.
Sources for this issue (1)
Theta III 2.5L T-GDI engines in GV80 JX1 (and related G80/GV70) illuminate the Check Engine light with random or specific cylinder misfire codes P0300-P0304 during cold start. Root cause is identified as ECM misfire-detection logic; Genesis issued service campaign 914G covering 2021-2024MY GV80 built 07/27/2020-03/04/2024 for a free ECM reflash.
Common Symptoms
- Check Engine Light on after cold start
- Rough idle during warm-up
- Brief stumble or shudder on first start of the day
- Multi-cylinder or cylinder-specific misfire codes
How to Fix
Free dealer remedy under Service Campaign 914G / TSB 25-01-051G: ~30 minute ECM software reflash with improved misfire logic. Persistent misfire after reflash warrants coil/injector swap-test on the affected cylinder.
Sources for this issue (1)
P0300 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0300 mean on a Genesis?
P0300 stands for "Random/Multiple Cylinder Misfire Detected." P0300 means the engine computer detected misfires occurring randomly or across multiple cylinders rather than in one specific cylinder. A misfire is when a cylinder fails to ignite its fuel-air mixture properly, which the computer senses through small fluctuations in crankshaft speed. Because it's not isolated to one cylinder, the cause is usually something that affects the whole engine — like fuel, air, or ignition system problems — rather than a single coil or plug. Persistent or heavy misfiring wastes fuel, runs rough, and can damage the catalytic converter, which is why a flashing check engine light should be taken seriously. On Genesis it is documented across 3 models: G90, G70, GV80.
What are the most common causes of P0300?
The most common causes of P0300 are: Worn or fouled spark plugs (across cylinders), Vacuum or intake air leak, Weak fuel pump, clogged fuel filter, or low fuel pressure, Failing ignition coils or worn spark plug wires, Dirty or faulty mass airflow (MAF) sensor, Clogged or dirty fuel injectors, Faulty crankshaft/camshaft position sensor, Low compression or EGR/PCV system faults. The specific cause varies by vehicle.
How much does it cost to fix P0300 on a Genesis?
Published repair estimates on Genesis range from $300 to $1,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0300 on a different make?
View P0300 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.