P0303 on 2021-2024 Genesis GV80: Cylinder 3 Misfire Causes and Fixes

What's Unique About the 2021-2024 Genesis GV80

The Genesis GV80, particularly with the 2.5L Turbo 'Theta III' engine, has a well-documented issue with cold-start misfires. Genesis acknowledged this by issuing a Technical Service Bulletin (TSB 25-01-051G) that resolves the problem with a simple software update to the Engine Control Module (ECM). This is an unusual and important first check for owners of the 2.5L model, as it can prevent unnecessary replacement of parts. While the 3.5L V6 can also experience misfires, it does not have the same software-related campaign; instead, some 3.5L owners have reported issues with faulty fuel injectors.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Rough or vibrating idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Check engine light is on and steady
• Check engine light is flashing (in severe cases)
• A smell of raw fuel from the exhaust
• Reduced fuel economy
• Engine stalling

Most Likely Causes

1. Engine Control Module (ECM) Software Needs Update 🔴 High Probability This specifically affects the 2.5L T-GDI engine. The manufacturer issued TSB 25-01-051G to address misfire codes (including P0303) that occur during a cold start. This is part of Service Campaign 914G.
   How to confirm: Contact a Genesis dealership and provide your vehicle's VIN. They can check if Service Campaign 914G (associated with TSB 25-01-051G) is open for your vehicle. The campaign is performed when the vehicle is in for any service.
   Typical fix: The dealership will update the ECM software with improved misfire logic. This is typically performed at no cost under the service campaign.
   Est. part cost: $0
2. Faulty Ignition Coil 🟡 Medium Probability Coil-on-plug systems are a common failure point on most modern engines. Heat and vibration can cause the coil's internal windings to fail over time. Some owners on forums have had this diagnosed as the specific cause for their P0303 code.
   How to confirm: Perform an 'ignition coil swap.' Turn off the engine, move the ignition coil from cylinder 3 to another cylinder (e.g., cylinder 1). Clear the codes and start the engine. If the code changes to P0301, the ignition coil is confirmed to be faulty.
   Typical fix: Replace the failed ignition coil. 🎬 Watch: Step-by-step guide to replacing a GV80 ignition coil Many technicians recommend replacing the corresponding spark plug at the same time.
   Est. part cost: $50-$100
3. Worn or Fouled Spark Plug 🟡 Medium Probability Spark plugs are a regular maintenance item. The high pressures in turbocharged direct-injection (GDI) engines can shorten their effective lifespan. A technician for a user on the r/GenesisGV70 subreddit noted a 'bllllackkkkk' spark plug when diagnosing a misfire.
   How to confirm: Remove the spark plug from cylinder 3. Inspect it for wear on the electrode, carbon fouling, oil residue, or cracks in the ceramic insulator. A heavily fouled plug is a clear indicator.
   Typical fix: Replace the spark plug. It is best practice to replace all spark plugs as a set to ensure consistent performance.
   Est. part cost: $25-$40 per plug
4. Clogged or Faulty Fuel Injector ⚪ Low Probability Gasoline Direct Injection (GDI) injectors operate under extremely high pressure and can be susceptible to clogging or electrical failure. There are multiple owner reports and technician videos for the 3.5L V6 GV80 showing misfires caused by failed injectors, sometimes with an open circuit detected in the injector coil.
   How to confirm: This requires more advanced diagnostics. A professional mechanic can perform a fuel injector balance test or check the injector's resistance with a multimeter. An open circuit (very high resistance) indicates a failed injector.
   Typical fix: The injector may be professionally cleaned. If it is faulty, it will need to be replaced. On the 3.5L V6, this is a more involved job. When replacing an injector, the high-pressure fuel pipes connected to it 🎬 See a technician diagnose multiple GDI injector failures should also be replaced as they are one-time use.
   Est. part cost: $150-$300

Rare But Worth Checking

• Coolant Leaking into Cylinder (3.5L V6): One documented case on a 3.5L V6 GV80 showed a misfire caused by coolant entering the cylinder, potentially from the water-cooled intercooler system. The technician in the video was initially puzzled by the presence of coolant but later could not replicate the leak, focusing on the injector instead. This remains a complex and very rare possibility that would likely present with other symptoms like unexplained coolant loss from the intercooler reservoir.
• Internal Engine Mechanical Failure: In very rare cases, a misfire can be caused by a loss of compression from a damaged piston, worn piston rings, or a faulty valve. While the newer 'Theta III' 2.5T and 'Lambda III' 3.5T engines are considered more reliable than their predecessors, isolated failures can still occur. A compression test and cylinder leak-down test would be required to diagnose this.

Diagnosis Steps

1. Read the Code: Use an OBD-II scanner to confirm P0303 is the only code present. Note any other codes, especially other misfire codes or air-fuel ratio codes.
2. Check for TSBs (2.5L Engine): If you have the 2.5L engine, your first step should be to contact a Genesis dealer with your VIN to see if the ECM update campaign (TSB 25-01-051G / Campaign 914G) is open for your vehicle.
3. Perform the Coil Swap Test: Switch the ignition coil from cylinder 3 with one from another cylinder (e.g., cylinder 1). Clear the codes and run the engine. If the code moves to P0301, the coil is bad and needs replacement. This is a common, easy diagnostic step.
4. Inspect the Spark Plug: If the code does not move, remove the spark plug from cylinder 3. Check for wear, damage, or fouling. A heavily fouled or damaged plug is a likely culprit. If it looks worn or dirty, replace it. It's recommended to replace all plugs as a set.
🎬 Watch: How to replace spark plugs on the V6 engine
5. Check the Fuel Injector: If the coil and plug are good, the issue may be the fuel injector. For the 3.5L V6 especially, this is a known issue. A professional can test the injector's resistance and flow rate. A DIY check could involve listening for a clicking sound from the injector with a mechanic's stethoscope to confirm it's activating.
6. Check for Mechanical Issues: If all else fails, a compression test and cylinder leak-down test should be performed by a professional to check for internal engine problems like bad rings or valves.

Parts You'll Likely Need

• Ignition Coil (OEM #27300-2T000 (For 2.5L T-GDI)) — A common failure point for misfires. The coil provides the high voltage needed to create a spark. Confirmed bad with a simple swap test.
  Trusted brands: Hyundai (OEM), Bosch, NGK
  OEM price range: $95-$135
  Aftermarket price range: $50-$100
• Spark Plug (OEM #18875-09085 (For 2.5L T-GDI), 18877-09085 (For 3.5L T-GDI)) — A standard wear-and-tear item. A worn or fouled plug cannot create a strong enough spark for proper combustion.
  Trusted brands: Hyundai (OEM), NGK
  OEM price range: $25-$40
  Aftermarket price range: $15-$30
• Fuel Injector (GDI) (OEM #35310-F01XX (Part number family for 3.5L, exact number varies)) — A notable failure point on the 3.5L V6 engine leading to misfires. Can fail electrically or become clogged.
  Trusted brands: Hyundai (OEM)
  OEM price range: $150-$250
  Aftermarket price range: Not widely available

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire Detected) may be stored alongside P0303. This is common with the 2.5L TSB issue.
• P0301, P0302, P0304 — If other cylinder-specific misfire codes are present, it points towards a problem affecting the entire engine, such as low fuel pressure, a major vacuum leak, or the ECM software issue on the 2.5L engine.
• P219E00 — This code for 'Cylinder #3 Air-Fuel Ratio Imbalance' can be stored alongside a misfire code. A TSB for the related Kia Carnival with the same 3.5L engine family suggests this combination points directly to a faulty high-pressure fuel injector.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin # 25-01-051G / Service Campaign 914G: Addresses misfire DTCs (P0300, P0301, P0302, P0303, P0304) on 2.5L T-GDI engines during cold start, fixed by an ECM software update. This TSB also applies to the Genesis G80 and GV70 with the same engine.

Platform-Specific Known Issues

• A Technical Service Bulletin (TSB 25-01-051G) was issued for 2021-2024 GV80 models with the 2.5L T-GDI engine for misfire codes (P0300-P0304) occurring on cold starts. The official fix is an update to the Engine Control Module (ECM) software.
• For the 3.5L Twin-Turbo V6, while no specific TSB exists for P0303, a pattern of fuel injector failures has been observed by technicians and owners, sometimes leading to persistent or recurring misfire codes.

Mechanic-Grade Diagnostic Values

• 3.5L GDI Fuel Injector Resistance — expected: ~2.2 Ohms. Failure: An open circuit (infinite or very high resistance) indicates a failed injector coil.
• Ignition Coil Primary Winding Resistance — expected: ~0.8 - 1.2 Ohms. Failure: A reading significantly outside this range, or an open circuit (OL), indicates a faulty primary coil winding.
• Ignition Coil Secondary Winding Resistance — expected: ~6 - 10 kOhms (kilo-ohms). Failure: A reading significantly outside this range, or an open circuit (OL), points to a failure in the secondary coil winding.
• Mode $06 Misfire Count per Cylinder — expected: A low count, ideally zero, during a test drive cycle.. Failure: A significantly higher misfire count for cylinder 3 compared to other cylinders, even if a P0303 code is not yet present. This can confirm an intermittent misfire.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID ~$A4: OBD-II Mode $06 provides access to non-continuous monitor test results. Misfire data for each cylinder is stored here. For a V6, the test IDs for misfire counts are typically $A2 through $A7. Test ID $A4 would correspond to cylinder 3. A technician can view the raw misfire count, which can identify a cylinder that is misfiring intermittently but not frequently enough to trigger a P0303 code. (see via An advanced OBD-II scan tool that supports Mode $06 data display.)

Scan Tool Commands That Help

• Genesis GDS-Mobile or equivalent bidirectional scanner: Cylinder Power Balance Test (or Fuel Injector Kill) — This is a powerful diagnostic step used when a misfire is suspected but the cause isn't obvious. The tool electronically disables one fuel injector at a time while the engine is idling. The technician observes the RPM drop for each cylinder. If disabling cylinder 3 causes little or no RPM drop compared to the other cylinders, it confirms that cylinder 3 was not contributing power, pointing to a problem with its fuel, spark, or compression.

Wiring & Ground Locations

• Cylinder 3 Location (3.5L V6) — Cylinder 3 is the middle cylinder on the passenger side (Bank 1) of the engine. The cylinders are numbered 1-3-5 on the passenger side (front to back) and 2-4-6 on the driver's side (front to back).. Correctly identifying cylinder 3 is the first step for any physical inspection or testing, such as swapping an ignition coil or inspecting a spark plug.
• Cylinder 3 Location (2.5L I4) — Cylinder 3 is the third cylinder from the front of the engine (the end with the accessory belts). The cylinders are numbered 1-2-3-4 from front to back.. Correctly identifying cylinder 3 is necessary to test the correct ignition coil, spark plug, and fuel injector.
• 3-Wire Ignition Coil Connector Pinout — The electrical connector on top of the ignition coil for cylinder 3.. When diagnosing a persistent misfire, a technician may need to test the coil's wiring. Pin 1 is typically the 12V+ power supply (key on), Pin 2 is the chassis ground, and Pin 3 is the trigger signal wire from the ECM. Verifying power, ground, and signal can rule out a wiring or ECM driver issue.

Real Owner Repair Stories

• YouTube channel of a professional technician (2021 Genesis GV80 3.5T) — Intermittent check engine light with a history code for P0302 (Cylinder 2 Misfire). The misfire was not always present.
  ❌ Tried (didn't work) Initial diagnosis was difficult because the misfire was intermittent. The technician suspected an injector based on a previous repair on the same vehicle.
  ✅ What actually fixed it The technician performed an ignition coil swap, moving the coil from the faulting cylinder #2 to cylinder #4. The customer drove the vehicle for a week, and the misfire code returned as P0304. This confirmed the ignition coil was faulty, and it was replaced, solving the issue. The video notes the same vehicle previously had a failed fuel injector with an open circuit.
• Reddit user in r/GenesisMotors (2024 Genesis GV80 3.5T Prestige, ~4,000 miles) — Check engine light and engine misfire.
  ❌ Tried (didn't work) Dealer initially reset the light, but it returned. A 'full diagnostic' found nothing. The dealer then replaced a fuel injector.
  ✅ What actually fixed it The issue was not fully resolved in the post. After the injector was replaced, the check engine light came back on, but this time for a 'knock sensor' code. The owner was initiating a vehicle buyback process. This story highlights that even after a common cause (fuel injector) is addressed, the diagnostic process can be complex.